The central nervous system (CNS) comprises of the brain and spinal cord. According to (Hull, 2011, p. 200) ‘it has three functions: sensory, integrative and motor.’ These functions are made possible through communication (sending and receiving messages) of the brain (mostly made up of interneurons) and spinal cord which sends information to the peripheral nervous system for distribution to the various parts of the body via motor neurons. The CNS senses and processes information, then responds to whatever message has been communicated.
The peripheral nervous system (PNS) consists of nerves (brain, cranial, spinal, afferent and efferent) running to and from the CNS. It comprises of the somatic (SNS) and autonomic (ANS) systems. The SNS controls voluntary activities of the body (skeletal muscle contractions or conscious reactions to sensory information processed by the body such as reaction to pain ‘ a single pathway of neurons responding to activation by excitatory impulses). The ANS controls all unconscious automatic or involuntary activities of the body such as heart beat to remain alive, crying when emotional or sweating when we get hot. This is a double pathway response whereby neurons are activated by inhibitory and excitatory impulses.
The ANS is subdivided into two further systems; the sympathetic and parasympathetic nervous systems. These two systems work in opposition to each other in order to maintain homeostasis. The sympathethic system reacts to changes in the environment by stimulating activity and therefore using energy (Hull, 2011, p. 204). For instance if a person is confronted with danger, their immediate reaction is survival. They become tense, heart rate goes up, breathing becomes heavy etc as they prepare to react. This is the ‘fight or flight’ response. The parasympathetic system will do the opposite to the sympathetic system by placing the person into a state of rest, calm and relaxation.
TAQ 1 total word count: 326/300 words
References
DLCentre notes, 2008/2010/2012. Human Biological Science 1: Coordination and Control.
Hull, R., 2011. Anatomy & Physiology for therapists and healthcare professionals. Cambridge: The Write Idea Ltd.
Tortora, G. and Derrickson, B. eds., 2011. Principles of Anatomy & Physiology. Asia: John Wiley & Sons.
TAQ 2
Figure 2 ‘ The three main types of neurons
Source: http://www.oocities.org/dtmcbride/science/biology/images/neuron-types.gif
Figure 3 – How the three main types of neurons interact
Source: http://vss.sd22.bc.ca/hpp/courses/bi12/ch17/Neurons.png
Neurons are nerve cells that carry information in the form of tiny electrical signals. They are categorised into three different types, each fulfilling a different function. Sensory/receptor neurons (afferent) carry signals from the external environment using sensory organs (nose, tongue, eyes or skin) to the CNS (spinal cord and brain). Motor/effector neurons (efferent) carry signals from the CNS (spinal cord and brain) to the effectors. Effectors are muscles or organs of the body that enact the messages that have been passed on by the brain. For example you might sense an itch on your arm and your brain sends a message to your muscles to move your hand over to scratch the itch with your fingers (a voluntary action).
Relay neurons (interneurons) are found within the CNS and carry messages from receptor neurons to effector neurons or from one relay neuron to another. They connect two neurons together (sensory and motor neurons).
References
BBC GCSE Bitesize, 2014. The nervous system. [online]. Available at:
http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/responses_to_environment/thenervoussystemrev2.shtml [Accessed 11 May 2014].
You Tube, n.d. BioVid Episode 2: An introduction to neurons. [online]. Available at:
https://www.youtube.com/watch?v=r5nMVAjz0d0 [Accessed 12 May 2014].
HPP Biology 12, n.d. Neurons. [online]. Available at:
http://vss.sd22.bc.ca/hpp/courses/bi12/ch17/Neurons.png [Accessed 12 May 2014].
Figure 4 ‘ Transmission of a nerve impulse: Resting and action potential
Source: http://media.wiley.com/assets/7/95/0-7645-5422-0_0704.jpg
Neurons are covered by cell membranes just like all cells and are semi-permeable (allow certain substances to pass (permeate) through them). The outside of the cell contains excess sodium ions the inside of the cell contains excess potassium ions (K+). Ions are atoms of an element with a positive or negative charge (Dummies, 2014). Neurons use electrochemical impulses to communicate with each other. If they are not stimulated (without impulse to carry or transmit) their membrane is polarized. Being polarized means that the electrical charge on the outside of the membrane is positive while the electrical charge on the inside of the membrane is negative (Dummies, 2014). Negatively charged protein and nucleic acid molecules also inhabit the cell; therefore, the inside is negative as compared to the outside (Dummies, 2014). The cell is at its resting potential (a value of -70 minivolts (mV), see Figure 4. This changes when an action potential with strong excitatory strength reaches the synapse and causes the ion channels to open and allow sodium ions to cross the cell membrane. K+ and Na+ pumps on the membrane allow these chemicals to still move back through the membrane allowing the cell to repolarise The more sodium ions enter the cell, the electrical potential of the cell changes so quickly that depolarisation occurs, meaning that the cell becomes positive again.
Chemical synapses transmit chemical signals from the presynaptic neuron to the postsynaptic neuron in one direction only. An electrical impulse or action potential’s arrival in the presynaptic neuron, is reaching the axon terminal. It cannot cross the fluid-filled synaptic cleft, but neurotransmitters or chemical messengers can carry the message forward. Ions (charged particles that allow change of electrical properties across the membrane) allow the messages to move on from one neuron to another or to an effector.
References
DLCentre notes 2008/2010/2012. Human Biological Science 1: Coordination and Control.
For Dummies, 2014. Understanding the transmission of nerve impulses. [online]. Available at: http://www.dummies.com/how-to/content/understanding-the-transmission-of-nerve-impulses.html [Accessed 12 May 2014].
National Institute of Health, n.d. The Brain: Understanding Neurobiology ‘ How neurotransmission works. [online]. Available at:
http://science.education.nih.gov/supplements/nih2/addiction/activities/lesson2_neurotransmission.htm [Accessed 12 May 2014].
b)
A synapse is a gap between adjacent nerve cells where impulses must be able to cross. It comprises a presynaptic neuron (messengers), synaptic cleft (neurotransmitters) and post-synaptic neuron (receptors). Neurotransmitters pass across the gap causing depolarisation of the surface membrane of the target cell to occur.
Figure 4 – Structure of the Synapse
Source: http://vss.sd22.bc.ca/hpp/courses/bi12/ch17.html
c)
Neurons have two major functional properties: irritability ‘ the ability to respond to a stimulus and convert it into a nerve impulse; and conductivity ‘ the ability to transmit the impulse to other neurons, muscles or glands (Marieb, 2009, p. 237). Neurotransmitters (chemicals) are what make these functions possible. They carry impulses in one direction from a cell’s dendrites to another. The dendrites of each neuron do not come into contact (the neurons do not touch) but the gap of the synaptic cleft allows the neurotransmitters to move freely across to the target cell. See Figure 4.
Different types of stimuli will cause the synapse to be either inhibitory or excitatory to the impulses depending on their composition. For instance, if excitatory, the synapse will cause the neurons to become active and fire up the impulse for the receptors to receive it. For example; sound causes some ear receptors to respond. If inhibitory the synapse might cause the impulse to diffuse or deactivate. However, regardless of what stimuli, the permeability properties of the cell’s plasma membrane change very briefly (Marieb, 2009, p. 237).
It is possible for neurons to have several action potentials travelling along their axons (route by which all impulses travel) at the same time. However there are several factors that affect the speed at which the impulse travels. For instance; impulses travel faster in myelinated (covered in myelin sheath) neurons; temperature affects the speed of conduction of impulses; and impulses are generally faster in an axon with a larger diameter (Biology.net). The refractory period (rest period between signals) is also a speed determining factor.
After the neurotransmitter has transmitted an impulse, it is released by the receptor and goes back into the synapse (Dummies, 2014). It is stored in the synaptic vesicles. Here the cell "recycles" the degraded neurotransmitter. The chemicals go back into the membrane so that during the next impulse (action potential), when the synaptic vesicles bind to the membrane, the complete neurotransmitter can again be released for another episode of impulse transmission (Dummies, 2014).
References
Biology Guide, n.d. Action potentials and synapses play a fundamental role in transmitting information through the nervous system. [online]. Available at: http://www.biologyguide.net/bya7/bya7-16-7.htm [Accessed 13 May 2014].
DLCentre, 2008/2010/2012. Human Biological Science 1: Coordination and Control.
For Dummies, 2014. Understanding the transmission of nerve impulses. [online]. Available at: http://www.dummies.com/how-to/content/understanding-the-transmission-of-nerve-impulses.html [Accessed 12 May 2014].
Marieb, E. N., 2009. Essentials of human anatomy & physiology. 9th ed. London: Pearson International.
Tortora, G, J. and Derrickson, B. eds., 2011. Principles of Anatomy & Physiology: volume 1 & 2. Asia: John Wiley & Sons.
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TAQ 4
Figure 6 ‘ Reflex Arc – Cross section of spinal cord showing a receptor’s reaction to flame
Source: http://leavingbio.net/the%20nervous%20system_files/THE%20NERVOUS%20SYSTEM_files/image028.gif
Thain (2009) describes the reflex arc as ‘the neural circuitry involved in a motor reflex, comprising a sensory neuron, a motor neuron and usually one or more interneurons (excitatory or inhibitory) interposed between these two’. It is a rapid protective behaviour involving taking voluntary action such as pulling a finger away from exposure to a flame as shown in Figure 6. Here, a pain receptor in the finger transmits signals via a sensory neuron to the spinal cord where the message is received by interneurons, which respond by sending signals back to the affected area via a motor neuron with information about what response to activate. In this case the response is to contract the muscles and move the finger away from the flame. This is a voluntary action where the brain makes a note of what happened and retains the information should it be required for any such experiences in the future.
Reference
Thain, M., 2009. Penguin Dictionary of Human Biology. London: Penguin Books.’
TAQ 5
Name of endocrine gland Location Hormones released Function (s) of hormones released
Pituitary -divided into two parts:
Anterior lobe
Posterior lobe
Base of brain beneath the hypothalamus
Growth hormone (GH)
Thyrotropin (TSH)
Prolactin
Adrenocorticotropic (ACTH)
Antidiuretic (ADH)
Oxytocin
Stimulates growth of other tissues including bone, maintains nutrients and minerals, inform reproductive system to make sex hormones, control ovulation and menstrual cycle in women
Stimulates production of the thyroid hormone by the thyroid gland
Stimulates production of milk in breastfeeding women
Stimulates production of specific hormones by the adrenal gland
Controls balance of water in the body
Triggers contractions of the uterus during childbirth, production of milk by the mammary glands to produce milk
Thyroid Trachea, beneath the larynx Triiodothyronine (T3) and Thyroxine (T4) Increases rate of metabolic and chemical reactions in body tissues, activates CNS, vital for bone growth and brain development
Parathyroids Attached to the posterior of the thyroid Parathyroid hormone (parahormone) Increases calcium levels in blood released from bone tissue, allows re-absorption in the kidneys
Thymus Mid chest cavity Thymosins Produces and matures T lymphocytes
Adrenal (medulla)
Adrenal cortex Inner area of abdomen, one on top of each kidney
Outer area of abdomen Epinephrine (adrenalin)
Norepinephrine (noradrenalin)
Cortisol
Increases blood pressure and heart rate during stress (‘fight or flight’ response)
Constricts blood vessels and increases heart rate in an emergency response
Regulates salt and water balance in the body, manages response to stress, breakdown of protein, fat metabolism, sexual development and immunity
Pancreas Abdomen
Abdomen Glucagon
Insulin
Maintains balance of glucose levels in the blood, stimulates glucose release from the liver
Regulates level of sugar glucose in the blood, essential for cells to utilize glucose
Ovaries Pelvis
Pelvis
Oestrogen
Progesterone
In puberty, aids in development of female sex organs and function, growth spurt. Development of ovarian follicles, bones and muscle contractions of the uterus, regulation of menstrual cycle and useful during pregnancy
Regulates menstrual cycle, generates secretions for the endometrium
Testis Pelvis Testosterone
Aids in development of male sex organs and characteristics in puberty, produces sperm
References
BBC GCSE Bitesize, 2014. Hormones. [online]. Available at:
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/human/hormonesrev1.shtml [Accessed 13 May 2014].
DLCentre, 2008/2010/2012. Human Biological Science 1: Coordination and Control.
InnerBody, 2013. Endocrine System. [online]. Available at:
http://www.innerbody.com/image/endoov.html [Accessed 13 May 2014].
TeensHealth, 2014. Endocrine System. [online]. Available at:
http://kidshealth.org/teen/your_body/body_basics/endocrine.html [Accessed 12 May 2014].
Tortora, G, J. and Derrickson, B. eds., 2011. Principles of Anatomy & Physiology: volume 1 & 2. Asia: John Wiley & Sons.
TAQ 6
Metabolism is a process whereby nutrients become involved in an incredible variety of biochemical reactions inside the body cells (Marieb and Hoehn, 2010, p.918). This is necessary to maintain energy levels and all bodily functions. Enzymes in the digestive system break down the food we eat and convert it into this energy. Metabolism occurs to balance our current needs against future needs of energy, knowing when to store or replenish it. This is achieved via two processes: anabolism (constructive metabolism) which involves the building up of complex chemical substances from smaller, simpler components; and catabolism (destructive metabolism) which is the breaking down of complex chemical substances into simpler components (Tortora and Derrickson, 2011, p. 5-6). For example proteins are broken down into amino acids and rebuilt to make new structures like muscle and bone through the catabolism and anabolism processes (Tortora and Derrickson, 2011, p. 7).
There are many different chemicals in cells and all have an effect on metabolism.
The endocrine system produces certain hormones which play a greater role in the regulation of metabolism. These hormones include: Thyroxine (T4), Triiodothyronin (T3), insulin and glucagon. T4 and T3 are thyroid hormones which mainly regulate our basal metabolic rate (BMR) ‘ the speed of metabolism and is involved in the amount of energy the body requires to maintain function and stay alive e.g. movement and heart-beat. BMR increases as the blood levels of thyroid hormones rise. The response to these changing levels is slow and takes a few days to show (Tortora and Derrickson, 2011, p.1049).
Insulin is released in the pancreas responding to raised levels of glucose after a meal. This signals cells to increase their anabolic activities i.e. increase glucose to transport receptors to the cell membrane as in contracting muscles or may mean the liver has an increased concentration of glucose therefore releasing glycogen as a short-term response into the blood. Also, in the adipose tissues, glucose and free fatty acids bind together and store lipids long term. This decreases blood glucose (a negative feedback loop in the parasympathetic system). Amongst other hormones, insulin can increase the metabolic rate by 5 ‘ 15% (Tortora and Derrickson, 2011, p.1049).
In starvation or stress conditions the body is very active, blood sugar levels drop, prompting alpha cells in the pancreas to release glucagon which helps stop glucose travelling around the body and focuses on providing energy for the brain. Glycogen breaks down into amino acids and glycerol in the liver produces new glucose by gluconeogenesis or lipolysis. Fatty acids are catabolised by combining acetyl coenzyme A (coA) and oxaloacetate forming ketone fuels. Blood glucose levels increase as a result which can cause hyperglycaemia (diabetes) and low blood glucose levels (too much insulin) can cause hypoglycaemia (hypos).
References
DLCentre, 2008/2010/2012. Human Biological Science 1: Coordination and Control.
Marieb, E. N., 2009. Essentials of human anatomy & physiology. 9th ed. London: Pearson International.
Tortora, G, J. and Derrickson, B. eds., 2011. Principles of Anatomy & Physiology: volume 1 & 2. Asia: John Wiley & Sons.
TAQ 7
The ear allows us to hear a range of different sounds as well as maintain our balance through head movement and position. Although the two organs serving these two senses are structurally interconnected within the ear, their receptors respond to different stimuli and are activated independently of one another (Marieb and Hoehn, 2011, p. 574).
It is connected to the brain by the auditory nerve and is subdivided into three major parts: the external (outer) ear, middle ear and internal (inner) ear. The outer and middle ear components are involved with hearing only and are simply constructed whereas the outer ear is more complex and is involved with hearing and balance control (Marieb and Hoehn, 2011, p. 574).
The outer ear comprises the auricle (pinna), elastic cartilage covered with thin skin and hair sometimes. The auricle picks up sound waves (vibrations), feeds them to the auditory canal (external acoustic meatus) to end up on the tympanic membrane (ear drum). Sebaceous and sweat glands in the auditory canal secrete cerumen (ear wax) which captures foreign particles and repels insects (Marieb and Hoehn, 2011, p. 574).
Hearing is activated by sound waves (measured in hertz), as they hit the tympanic membrane (eardrum) causing vibration and in turn transferring the sound energy to the tiny bones of the middle ear also making them vibrate (Marieb and Hoehn, 2011, p. 574). The middle ear is located in the skull’s temporal bone. Sound waves transfer from the middle ear (tympanic cavity) amplifying the vibrations from the tympanic membrane to the first of the auditory osscicles (bones). The malleus (hammer) connected to the tympanic membrane, passes vibrations onto the incus (anvil), the stapes (stirrup) and onto the oval (vestibular) window
The middle ear is air-filled and can sometimes be consumed with pressure (when on a plane) which can be released via the pharyngotympanic (auditory) tube linking the middle ear cavity with the pharynx (throat) and the mucosa of the middle ear that lines the throat (Marieb and Hoehn, 2011, p. 574). Swallowing or yawning opens the usually flattened auditory tube to balance the pressure in the middle ear with external air pressure, important for the eardrum to vibrate freely without distorted sound (Marieb and Hoehn, 2011, p. 574).
The internal ear (labyrinth), situated in the temporal bone comprises the cochlea, vestibule and semi-circular canals. Vibrations come from the oval window into the cochlea then fibres transmit electrical impulses via the ganglia to the organ of corti which translate that stimulation into nerve cell excitation and neurotransmitters transmit back to the auditory cortex of the brain along the auditory nerve (DLCentre, 2008/2010/2012). Perilymph and endolymph fluids conduct the sound vibrations involved in hearing and respond to the mechanical forces occurring during changes in body position and acceleration (Marieb and Hoehn, 2011, p. 576).
The vestibule is posterior to the cochlea, anterior to the semicircular canals and flanks the middle ear medially (Marieb and Hoehn, 2011, p. 576). It is responsible for balance and posture. The utriculus and semicircular canal within detect tilting movements in relation to gravity and help keep the body upright. Communication to the brain is via the vestibular nerve
The eye lets us see by detecting visible light (part of electromagnetic spectrum ‘ wave energy that radiates from the sun). Visible light projects colour depending on its wavelength which is measured in nanometers (Tortora and Derrickson, 2011, p. 642).
The eye comprises accessory structures (eyelids, eyelashes, eyebrows, the lacrimal (tear producing) apparatus and extrinsic eye muscles) that protect and move the eye and eyeball structures. The eyeball is divided into the anterior and posterior chambers. Three most visible components of the anterior chamber are: the pupil (dark dot at centre of eye allowing light onto retina); the iris (covers the pupil, colour pigmented and light regulator); and sclera (orb-like shaped white, elastic substance encasing the cornea, moistened and protected by conjunctiva),
The cornea, (transparent, dome-shaped, and protruding from the sclera) helps direct and focus light. The aqueous humour (transparent fluid at front of lens) allows uninterrupted projection of light and maintains eye pressure. Other components include the sphincter and dilator muscles which control the size of the pupil, the ciliary body, suspensory ligaments and ciliary smooth muscles which support the lens
The posterior chamber contains components that give focus to an image. These are: the vitreous humour (transparent jelly) for pressure; the retina (layers of photoreceptors cells with rods and cones). Up to 130 million rod cells allow us to see in black and white, in dim or low light and assist with perception of objects. Up to 10 million cone cells allow us to see in colour (blue, green and red) and bright, higher intensity light waves (DLCentre, 2008/2010/2012). Having no photoreceptors at the optic nerve site creates ‘the blind spot’ (optic disc),
The visual cortex is the final destination for visual information. Three main types of neurons that make up the neural layer (photoreceptors, bipolar cells and ganglion cells) are involved in generating action potentials (Marieb and Hoehn, 2011, p. 552). Processed information is then transported to the brain from the optic nerve fibres through the optic chiasm, collecting and reducing the impulses in the optic tract towards the thalamus then the occipital lobe before interpretation of incoming signals occurs in the visual cortex
References
DLCentre notes, 2008/2010/2012. Human Biological Science 1: Coordination and Control.
Marieb, E. N., 2009. Essentials of human anatomy & physiology. 9th ed. London: Pearson International.
Tortora, G, J. and Derrickson, B. eds., 2011. Principles of Anatomy & Physiology: volume 1 & 2. Asia: John Wiley & Sons.
‘
Bibliography
British Medical Association, 2013. Illustrated Medical Dictionary. 3rd ed. London: Dorling Kindersley.
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