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Animal Science
ANSC 2340
Ira Mandell

LEC 11 : Pg. 324-328 The Brain and Spinal Cord:  Divided into 4 separate sections: cerebrum, cerebellum, diencephalon (“between brain”), and brain stem.  The brain stem and diencephalon are the most primitive parts  Cerebellum coordinates motor control  Highest center of function found in the cerebrum  Disease in each part of the brain produces different clinical signs Cerebrum:  Is made up of the gray matter of the Cerebral Cortex (outer layer of brain) and white matter fibres beneath the cortex, incl. the corpus callosum (set of fibres connecting 2 halves of the cerebral cortex)  Largest part of the brain in domestic animals, associated w/ functions associated with higher order behaviours (learning, intelligence, awareness etc.)  Receives & interprets sensory info; intakes conscious (voluntary) nerve impulses to skeletal muscles; & integrates neuron activity associated w/ communication, expression of emotion, learning, memory and recall  It’s wrinkle appearance on the surface is due to the folds called gyri separated by grooves called fissures & shallower grooves called sulci.  Prominent groove= longitudinal fissure (divides cerebrum into right & left cerebral hemispheres)  Each hemisphere is divided by sulci into lobes (diff. lobes specify diff. functions)  E.g. front half of the brain initiate voluntary motor functions, & posterior lobe to this section identifies the locations of sensation in or on the body Cerebellum  Located caudal to the cerebrum , second largest component of the brain  Allows body to have : coordinated movement, balance, posture & complex reflexes  It compares the movement the body intends to make w/ the actual position of muscles & joints to determine if the intentions of the cerebral cortex are actually being carried out  If movements not carried out: cerebellum stimulates muscles to fine-tune the movements  When flexing arm, stretch receptors associated w/ the muscles send feedback to the cerebellum to keep it informed on the position of the arm  In addition to making voluntary body movements smooth & accurate, it also uses this same sensory feedback from the muscles to maintain posture and balance.  Hypermetria - damage or disease of cerebellum, results in voluntary movements that become jerky & exaggerated (occurs in pigs, develop a goose-step gait & in any young of other species with under- developed cerebellum). Diencephalon  Not as physically defined as the cerebrum & cerebellum  Serves as a nervous system passageway between the primitive brain stem & the cerebrum (hence common name= between brain)  Associated structures: 1. Thalamus: acts as a relay station for regulating sensory inputs to the cerebrum 2. Hypothalamus: interface between the nervous system & the endocrine sys. (also: role I temp. regulation, hunger, thirst, & rage/anger responses) 3. Pituitary: the endocrine “master gland” that regulates hormone production & release throughout the body Brain Stem  Connection btwn. the rest of the brain & the spinal cords  Stem of which the other parts of the brain sit  Most primitive part of the brain composed of: the medulla oblongata, the pons & the midbrain  It’s role is to maintain basic support functions of the body , operating at the subconscious level  Heavily involved in autonomic control functions related to heart, respiration (incl. coughing, sneezing & hiccupping), blood vessel diameter, swallowing & vomiting  Many cranial nerves originate from this area  Damage to the brain stem can result in the animal dying rapidly from respiratory failure or cardiovascular collapse.  Fortunately it is well protected by the skull, so brain stem injury is rare, unless major damage to the skull occurs Meninges  Set of connective tissue layers that surround the brain & spinal cord  The 3 layers of the meninges- from outside to innermost layer  The tough, fibrous dura mater; the delicate , spiderweb-like arachnoid, and the very thin pia mater which lies directly on the surface of the brain & the spinal cord  These connective tissue layers contain a rich network of blood vessels that supply nutrients & oxygen to the superficial tissues of the brain & spinal cord  The fluid, fat & connective tissue found between the layers of the meninges also provide some cushioning & distribution of nutrients for the CNS  Meningitis= inflammation of these meningeal membranes from virus or bacteria Cerebrospinal Fluid  The brain & spinal cord are bathed & protected from the hard inner surfaces of the skull & spinal column by this fluid (CSF)  Clear, slippery CSF circulates btwn layers of the meninges & through cavities (canals & ventricles) inside of the brain (ventricles) & the spinal cord ( central canal)  It’s chemical composition may be involved in regulating certain autonomic functions , such as respiration & vomiting  E.g. if pH of the CSF becomes more acidic, respiratory center in the brain stem will INC resp. rate  Because CSF circulates throughout the CNS, infection, inflammation, or cancer in the brain or spinal cord can cause CSF to change the amount of protein it contains; can also change the composition of its cells, incl. white blood cells or cancer cells Blood-Brain Barrier  Functional barrier separating the capillaries In the brain from the nervous tissue itself  These capillary wall cells in the brain are aligned tightly together without these openings or fenestrations & are covered by the cell membranes of glial cells ; this results in a cellular barrier preventing many drugs, proteins, ions & other molecules from readily passing from the blood into the brain  The blood-brain barrier protects the brain from many poisons circulating in the bloodstream Cranial Nerves  Special set of 12 nerve pairs in the peripheral nervous system numbered in roman numerals from I through XII (refer to pg.327 for a table of all these & pg.228 for MNEMONIC device!)  The cranial nerve itself may contain axons, of motor neurons, axons of sensory neurons or combinations of both  CN I- olfactory nerve & CN II- optic nerve : both examples of pure, sensory cranial nerves  Olfactory nerve is responsible for conveying sensory from receptors in the nose to the brain for the sense of smell  Optic nerve is responsible for perception of light & vision  CN III is the oculomotor nerve; motor cranial nerve that controls eye movement, pupil size, focusing lens  CN IV trochlear , motor , eye movement  CN V : trigeminal nerve, sensory & motor; control muscles of the jaw for chewing & also convey sensations from the nose, mouth,& part of the throat MNEMONIC DEVICE for the NERVE NAME: On Old Olympus’ Towering Top, A Fine Vocal German Viewed Some Hops! Olfactory ; Optic; Oculomotor; Trochlear; Trigeminal; Abducent; Facial; Vestibulocochlear; Glossopharyngeal; Vagus; Spinal accessory; Hypoglossal For the TYPE OF NERVE: Six Sailors Made Merry, But My Brother Said “Bad Business, My Man” Sensory; Sensory; Motor; Motor; Both (sensory & motor); Motor; Both; Sensory; Both; Both; Motor; Motor Spinal Cord  Is the caudal continuation of the brain stem outside the skull that continues down the bony spinal canal formed by the vertebrae of the spine  Conducts sensory info & motor instructions btwn the brain & the periphery of the body  Contains many neuron cell bodies (in the gray matter) & extensive synapses (connections) btwn ascending nerve fibres conducting sensory info going to muscles & other organs  Lots of processing & modification of nerve impulses btwn the brain & peripheral nerves takes place in spinal cord (SC)  Gray matter of the SC is located at the center of the medulla & take the shape of a butterfly w/ the central canal at its center  White matter (contains myelinated nerve fibres) of the SC forms the cortex (outer part) surrounding the gray matter  Btwn each adjacent vertebrae, the SC sends off dorsal & ventral nerve roots from each side that combine to form left & right spinal nerves; linking the SC w/ peripheral nerves  Dorsal Nerve Roots: contain Sensory (afferent) fibres – where sensory info enters the SC  Ventral Nerve Roots: contain Motor (efferent) fibres- where motor instructions go out  The neurons that forward sensory nerve impulses to the brain or other parts of the SC are located in the Dorsal Horns of the SC’s gray matter “butterfly”  The neurons that forward motor impulses to the spinal nerves are located in Ventral horns of the gray matter LEC 12 P.314-324, pg.328-332  The nervous system is a complex communication & control system  Monitors internal and external environments & directs activities to maintain the well-being of the body  Structurally has 2 Main divisions: the CNS (central nervous sys) & PNS (peripheral nervous sys)  CNS : composed of the brain & spinal cord  PNS : consists of cordlike nerves that link the CNS with the rest of the body  Functionally has 3 Categories: 1) sensory functions, 2) integrating functions, 3) motor functions  The NS senses changes within or outside the body and conveys this info to the spinal cord & brain; then the sensory info is received, analyzed, stored, & integrated to produce a response  Motor response instructs the body to do something like contract a muscle or cause gland to secrete product  Study of nervous sys= neurology Neurons & Supporting Cells  Neurons: (nerve cells) the basic functional units of the NS , they are the smallest pieces of the sys that show basic NS functions . they are high maintenance  have a high requirement for oxygen  need a great supporting cast to be successful. Glial cell: structurally & functionally support & protect the neurons (out number neurons 10:1)  Dendrites: receive stimuli, or impulses from other neurons & conduct simulation to the body (extend from the cell body)  Dendrites can also be modified into sensory receptors (to heat, touch ect)  Axons: conduct nerve impulses away from the cell & toward another cell or an effector cell ( cell that does something when simulated)  Myelin: fatty substance that covers axons  Myelin sheath: the cell membrane of specialized glial cells (oligodendrocytes) in the brain & spinal cord  Myelin sheath & node of Ranvier act together enhance the speed of conduction of nerve impulses along the axon  Cranial nerves: nerves of the PNS that originate directly from the brain  Spinal nerves: nerves of the PNS that emerge from the spinal cord  Afferent nerves: conduct nerve impulses TOWARDS from the CNS (also called sensory nerves)  Efferent nerves: conduct nerves impulses AWAY from the CNS (also called motor nerves)  Somatic NS: voluntary initiation (conscious) ; impulses being sent to the CNS from receptors in the muscles, skin, eyes or ears (consciously perceived by the brain)  Autonomic NS: involuntary; heart rate, contracting intestines, blood pressure ect. Send impulses to smooth muscle, cardiac muscle & glands for regulation  Resting state= when neuron isn’t being stimulated (but is still working to maintain its resting state)  The cell membranes of neurons are electrically polarized at rest like tiny batteries Sodium-potassium pump: causes higher conc of sodium outside of the cell (sodium can’t diffuse easily). This creates negative charges inside the cell creating a high conc. Of potassium inside the cell. This separating of sodium outside & potassium inside is said to be POLARIZED (has 2 distinct poles of ions on either side of the membrane)  Resting membrane potential= electrical difference in charges across the membrane (the cell membrane “battery” is charged  When an impulse from an adjoining neuron or specific type of external stimulus (heat, touch or taste) results in the nerve “firing” or depolarizing  This causes sodium channel on the membrane to open and sodium to flow into the cell , attracted by the negative potassium inside  Depolarization: refers to the opening of the sodium channels & sudden influx of many sodium ions into the cell (gets a net positive charge)  Action potential: the significant change in electrical charge from NEG -> PO  a fraction of a second later, the sodium channels snap shut , halting the influx & the potassium channel opens back up , & the K+ ions passively diffuse out of the cell  Remember like charges REPEL, therefore when sodium comes in, potassium wants out  Repolarization: change if the cell’s charge back toward the net neg resting membrane potential (only diff is they are now on opposite sides of the membrane, the pump fixes this by quickly moving the misplaced ions back to their normal sides)  Threshold: when the stimulus is strong enough to cause complete depolarization , this causes the cell to “fire”  Threshold stimulus: a stimulus of sufficient intensity to generate a nerve impulse  Weak stimulus would result in the info from the sensory receptors after repolarization to not be transmitted to the brain  Wave depolarization: wave of sodium channels opening to allow sodium influx (or the conduction of the action potential) these waves along the cell membrane are called Nerve Impulses  All or Nothing principle: either the complete neuron depolarizes to its max strength, or it doesn’t depolarize at all  Refractory period: “insensitive” to new stimuli until it recovers from the previous nerve impulse (absolute refractory period: cell cannot respond at all)  Relative Refractory Period: cell is still refractory to stimuli of normal intensity but may respond to relatively large stimuli  Saltatory conduction: rapid mean of conducting an action potential , depolarization wave skips from one node of ranvier to another , greatly accelerating the rate at which depolarization wave moves from the neuron cell body to the other end of the axon  Multiple sclerosis: myelin sheath are very damaged, conduction of impulses is much slower , loss in rapid communication  Synaptic transmission: the perpetuation of the nerve impulse from one neuron to the next cell  Synapse: the junction between 2 neurons or a neuron & taget cell; consists of a physical gap between the 2 cells = a synaptic cleft  Presynaptic neuron: the neuron bringing the depolarization wave to the synapse & releasing
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