7. Nervous System PDF

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Summary

The content of the work on organs, specifically the nervous system is summarised in this document. Class notes, class slides and the book (Anatomy and Physiology of Farm Animals, Rowen D. Frandson, W. Lee Wilke & Anna Dee Fails. Seventh Edition) was used to complete these summaries. Colour was used ...

Description

Nervous System: Nervous System:  Nervous System: The master controlling & communicating system of the body. An organ system containing a network of neurons (specialized cells).  Nervous System Functions:  Sensory Input  Sense stimuli occurring inside & outside the body.  Integration  Interpretation of sensory input  Motor Output  Response to stimuli by activating effector organs

 Central Nervous System (CNS): Includes brain & spinal cord  Peripheral Nervous System (PNS): Connects nerves running from the brain & spinal cord to the rest of the body (arms, hands, legs, feet, organs, joints, mouth, eyes, ears, nose & skin).  Autonomic NS:  Conducts impulses from CNS to ORGANS for response  Regulates all reflexes of importance controlling organ functions  Controls smooth muscles, heart muscles & glands unconsciously  no stimulus!  Sympathetic NS: o Dilates pupils, relaxes bronchi, accelerates heartbeat, inhibits digestion & contracts vessels o Most neurons release non-epinephrine o Informs body of flight/fright situation ( heart rate &  BP)  Parasympathetic NS: o Contracts pupils, constricts bronchi, slows heartbeat, stimulates digestion & dilates vessels o Releases acetylcholine o More relaxed situation  Somatic NS:  Conducts impulses from CNS to SKELETAL for response  Requires a stimulus

Neurons:  Neuron (nerve cell): Co-ordinates actions of an animal & transmits signals between different parts of the animal body. Highly irritable & sensitive.  Neuron is the functional unit of the nervous system!  Neuron Functions:  Responds to stimuli (touch, sound & light)  Conducts impulses & communicates with each other (& other types of cells  muscle cells)  Neurons vary in length & size

 Each neuron has a cell body & extending from it are processed (outgrowths)  dendrites & axons  Neuron has many dendrites, but only 1 axon

Nerve Synapse:      

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Nerve Synapse: Specialized connection between 2 neurons/a neuron & a muscle/a gland. Only operates in 1 direction (orthodromic conduction)! Transfer over a synapse occurs with the help of acetylcholine (specific transfer medium) Site where nerve impulse is converted to chemical stimulus (acetylcholine  a neurotransmitter) that travels from 1 neuron (presynaptic) to another neuron (postsynaptic) across synaptic cleft In postsynaptic neuron, stimulus is converted back to a nervous impulse (electrical) Factors influencing impulse transmission (Rate at which impulses are transmitted): 1) Drugs acting at the synapse (sedatives) 2) Alkalosis ( in pH) 3) Acidosis ( in pH) 4) Lack of O2 ( in pH) 5) Diversion ( Rate of impulse conversion) 6) Conversion ( Rate of impulse conversion) Diversion: 1 neuron transmitting an impulse to several impulses. Conversion: Several impulses transmitting to 1 neuron.

Resting Membrane Potential:  Used to send & receive information  Membrane potential changes are produced by:  Changes in membrane permeability to ions  Alterations of ion concentrations across the membrane (Acidosis, Alkalosis)  Changes caused by:  Depolarization  Inside of the membrane becomes less negative (a fast  of membrane’s permeability to Na+)  Repolarization  Membrane returns to its resting membrane potential  Phases of Action Potential:  Ability of neuron to transform mechanical & chemical stimuli to electrical energy. 1) Resting State  Resting Membrane Potential 2) Depolarization Phase 3) Repolarization Phase  Back to Resting  Speed of Conduction:  For each fibre, speed stays the same  Different fibres have different speeds  depending on thickness of the fibre (thicker fibre = faster conduction)  Myelinated fibres conduct impulses at very high speeds = Saltatoric conduction  Consists of nodes of Ranvier = No myelin  highly permeable, causing impulses to jump from 1 node to another. At nodes membrane is directly in contact with extracellular fluid.  Myelin Sheath  Saltatory Conduction:  Current passage through a myelinated axon only at the nodes of Ranvier  Voltage-gated Na+ channels are concentrated at these nodes  Impulse jump from 1 node to the next  Saltatory Conduction  Much faster than conduction along unmyelinated axons

Reflex Action:  Reflex Action: Automatic/unconscious response of an effector organ to an appropriate stimulus. Includes chain of neurons, which form a reflex arc.  Reflex Arc: Neural pathway over which impulses travel.  Includes 5 components: 1) Sensory Receptor  Responds to stimulus 2) Afferent/Sensory Neuron  Transmits impulse to spinal cord 3) CNS  Processes info 4) Effector/Motor Neuron  Transmits impulse out of spinal cord 5) Effector  A muscle/gland that receives impulses from motor neuron & carries out a desired response Component

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Function

 Reflex Centres:  Medulla Oblongata  Regulation of heart action, blood vessels width & respiration  Cerebellum  For movement & posture  Hypothalamus  For temp. control & water balance (shivering, sweating & panting)  Cerebrum  Controls amount of light striking retina (pupil dilation/contraction) _______________________________________________________________________________...