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Module 6.docx

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Biology 3436F/G
Tim Hain

Module 6 - Central nervous system made up of the brain and spinal cord - Peripheral nervous system – nerves outside the CNS that go to muscles and organs (like heart) o Somatomotor – going to skeletal muscles o Autonomic – going to other organs - The brain contains between 10 billion to 100 billion cells and weighs about 1.5 kilos (3.5 lbs) o If all the cells were laid out end-to-end they would stretch 1000 km (600 miles) o You have more brain cells when you are born o Action potentials can travel down nerve cells at up to 400 km/h (240 mph) - Brain has 2 cerebral hemispheres (left and right) o Left sends signals to activate muscles on the right side of the body and sensory info on the right side of the body travels to the left hemisphere (and vice versa) o Brain stem controls most basic functions (heart rate, respiration) and is made up of the midbrain, pons and medulla o Medulla is continuous with the spinal cord o Cerebellum – at the posterior just above the brain stem – responsible for coordinated movement o Diencephalon – consists of the thalamus and hypothalamus o There are many bumps (called gyri) and dips (called sulci) on the brain surface – most prominent in humans, increase surface area – locations of these consistent between individuals with minor differences in size and shape  Cerebral hemisphere can be divided into 4 lobes based on these landmarks  Each lobe are regions that have specific functions  Frontal lobe – primary motor cortex processes input from skeletal muscles throughout the body while the motor association areas (premotor cortex) and prefrontal cortex integrate movement information with other sensory inputs to generate perception/interpretation of stimuli • Primary motor cortex – posterior end of frontal lobe, process info relating to skeletal muscle movement – when stimulated will cause specific muscles to contract, arrangement specific  Temporal lobe – primary auditory cortex and auditory association areas which receive and process signals from the auditory nerve and integrate them with other sensory inputs – other parts involved in olfaction (smell) and in mediating short term memory storage and recall  Occipital lobe – cerebral cortex, responsible for vision – contains primary visual cortex which receives input directly from the optic nerve as well as visual association areas that further process visual info and integrate it with other sensory inputs  Parietal lobe – primary somatosensory cortex – receives input from major sense organs (skin, musculoskeletal system, taste buds) – association areas integrate sensory info with other association areas of the cortex to form meaningful perceptions • Primary somatosensory cortex – receives sensory info from opposite side of the body – sensations like pain, temp, touch and vibration processed here  Cerebellum – processes sensory info and coordinates the execution of movement in the body – largest number of neurons, receives input from somatic receptors, receptors for equilibrium and balance and motor neurons from the cortex • cerebellum functions include generations of accurate limb movements, correcting ongoing movements and modifying the strength of some reflexes • also involved in pavlovian conditioning, the learning of new muscle movements and vestibular occular reflex (VOR) one of our important eye movements • must receive info from 2 different sources: must receive the same info from the motor cortex that is travelling out to the muscles being activated and it must receive information dealing with the position of the limbs in space (proprioception) • compares actual signal from brain w/ proprioceptive info from muscle – makes sure muscle is doing what it is supposed to, if not it will modify signals from the primary motor cortex  Corupus callosum – dense bundle of nerve fibers that serves as a pathway and connection between the 2 cerebral hemispheres – connection allows the brain to integrate sensory and motor info from both sides of the body and to coordinate whole-body movement and function  Diencephalon – thalamus receives sensory input as it travels from the spinal cord and integrates sensory info before sending it to the cortex; hypothalamus controls a variety of endocrine functions (body temperature, thirst, food intake, etc..) mainly through directing the release of hormones  Pituitary gland – regulates other endocrine organs – anterior pituitary (hormones include: LH, FSH, ACTH, TSH, GH and prolactin) derived from epithelial tissue of the pharynx while posterior pituitary (hormones include: vasopressin and oxytocin) derived from neural tissues of the hypothalamus • Pituitary function regulated by the hypothalamus • Smallest part (size of pea), below hypothalamus  Midbrain (mesencephalon) – bridges lower brainstem with diencephalon above, primary function controlling eye movements – also exerts control over auditory and visual motor reflexes  Pons – relay station to transferring information between the cerebellum and the cerebral cortex – also coordinates and controls breathing along with centers in the medulla  Medulla – portion of brainstem with primary control over involuntary function (breathing, BP and swallowing) – here fibers from the corticospinal tract (originated from the motor cortex) cross over to the opposite side of the spinal cord to innervate muscles on the opposite side of the body  Optic nerves – from each eye meet at the optic chiasma where they cross over and continue on as optic tracts to the lateral geniculate bodies of the thalamus – from there axons extend to their respective hemisphere on the primary visual area of the occipital lobe  Brain stem – extension of the spinal cord – consists of the pons, midbrain and medulla – incorporates 9 cranial nerves, center of many involuntary functions  Language and mathematical area – usually located in the left hemisphere (even for left-handed people) – serves as a general interpretive center enabling a person to understand visual and auditory info and in turn to generate written and spoken responses - 3 types of neurons: o Bipolar neurons – 2 processes extending from the cell body, form of specialized neurons that can be found in the retina of the eye o Unipolar neurons – one process extending from cell body – located in peripheral nerves outside the CNS and are generally sensory in nature, transmitting signals down spinal cord – cell body lies in the middle and off to one side of the axon o Multipolar neurons – contain many branching dendrites and one axon – most common in the CNS - Glial cells are the support cells of the brain - maintain delicate internal environment of the CNS o 5 times as many glial cells as neurons o Structural role (gluing things together) and regulate nutrients and specific interstitial environment of the brain (regulate the passage of substances between the blood and brain’s interstitial space) o Different types of glial cells: astrocytes, microglia, oligodendrocytes (produce myelin) - Special receptors detect pressure on skin when holding an object, the weight of the object is coded into the AP – the heavier the object, the more AP per second  neural coding - Nerve cells communicate with one another by chemical synapse (presynaptic nerve will release a neurotransmitter that affects the postsynaptic nerve) o Axon terminal of the presynaptic cell contains: voltage gated calcium channels, synaptic vesicles and mitochondira o Presynaptic neurons synthesize neurotransmitters that are stored in synaptic vesicles o An action potential in the presynaptic neuron depolarizes the membrane and activates voltage gated calcium channels, calcium flows into the axon terminal o Calcium causes synaptic vesicles to fuse to the wall of the synaptic terminal causing exocytosis and the release of neurotransmitter o Neurotransmitter diffuses across the synaptic cleft and acts on chemical receptors found on the postsynaptic cell membrane (postsynaptic cell also contains chemically gated ion channels – opens when NT attaches to them) o Depending on the neurotransmitter, the response can be excitatory (leading to depolarization of the postsynaptic cell which if strong enough may fire an AP) or inhibitory (leading to hyperpolarization of the postsynaptic membrane making it harder to generate an action potential) - Similar to NMJ but at the chemical synapse a single action potential on a presynaptic neuron will NOT produce an AP on a postsynaptic neuron (in NMJ a single AP in motor nerve produces a single AP in muscle) o And excitatory NT will cause the opening of chemically gated channels (selective for positive ions, will allow the influx of mainly sodium ions)  local depolarization of the membrane called an excitatory postynapitc potential (EPSP), diminishes with time and distance from point of origin, also called a graded potential - Influx in Na+ does not fire an AP because there are no v
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