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The Nervous System and the Control of Movement Two Components 1. CNS (Central Nervous System) • brain and spinal cord 2. PNS (Peripheral Nervous System) • 12 pairs of cranial nerves and 31 spinal nerves CNS The brain: receives and interprets signals sent from other parts of the body 6 major parts Cerebrum • Largest • sensory and motor activities AND intelligence • Divided into frontal, temporal, parietal and occipital lobes Cerebellum • 2nd largest • movement and balance Brain Stem • Link between spinal cord and cerebellum • Posture, muscle tone, eye movement (autonomic functions) Diencephalon • Between cerebrum and brain stem • Thalamus and hypothalamus Thalamus: pain, screens signals, attention Hypothalamus: body temp., appetite, emotions other automatic function Limbic System • Structures in cerebral hemispheres • Regulates drives (hunger, aggressions etc.) Reticular Activating System • Network of neurons • Maintaining consciousness The Spinal Cord: main pathway for messages and connects brain to PNS • Travels down vertebral column to 2nd lumbar vertebrae • Adults 42cm-45cm long • Spinal nerves exit between vertebrae • Carries sensory info. to brain and motor info. away from brain PNS Recall; 31 pairs of spinal nerves and 12 pairs of crainial nerves - nerves have two roots 1. anterior root: carries motor nerve fibres (efferent) 2. posterior root: carries sensory nerve fibres (afferent) PNS 2 Components 1. • • Autonomic Nervous System Controls involuntary contraction 2 Subsystems 1. Sympathetic System - causes localized body adjustments to occur (sweating or cardiovascular changes) - prepares the body for emergencies (fight/flight) 2. Parasympathetic System - returns body to normal after sympathetic response 2. • • • • • Somatic Nervous System Awareness of external environment Afferent and efferent nerve fibres Info from receptors in the skin, voluntary muscles, tendons and joint Gives sensations in touch, pain, heat…. Movement See pg. 97 Figure 6.2 Reflex Arc Reflexes: automatic and rapid responses to particular stimulation Reflex Arc: the pathway along which the initial stimulus and the correcting response message travel cerebral reflex- command center in brain spinal reflex- command center in spinal cord Autonomic reflexes - mediated by autonomic division of nervous system - Smooth muscle, cardiac muscle, glands Somatic reflexes - mediated by somatic division of nervous system - Stretch and withdrawal reflex (ways the body responds to unexpected 5 Parts of a Reflex Arc 1. Receptor: receive the initial stimulus (pinprick/loud noise) 2. Sensory (afferent) nerve: sends impulse to spinal cord or brain (afferent neuron of muscle spindle or tendon organ) 3. Intermediate Nerve Fibre: interprets the signal and issues an appropriate response (interneuron) 4. Motor (efferent) nerve: carries response from spinal cord to muscle organ 5. Effector organ: carries out the response (skeletal muscle moves) Proprioceptors and Control of Movement • Provide sensory information about the state of muscle contraction, the position of body limbs, body posture and balance • Located in tendons, muscles, and joints • Two sensory receptors: – Golgi tendon organs – Muscle spindles Golgi Tendon Organs - sensory receptors that terminate where tendons join to muscle fibres - Used to detect tension exerted on tendon - 1 sensory nerve, 1 motor nerve - Play a part is strength and power development Muscle Spindles - sensory receptors that lie parallel to main muscle fibres - Send constant signals to spinal cord - 2 sensory nerve, 1 motor nerve - Help maintain tension and sensitive to muscle length - Play a part in all physical movement as they constantly and automatically adjust to the changing demands placed on them The Stretch Reflex - Simplest spinal reflex - Monosynaptic reflex - e.g knee jerk 1. Receptor muscle sense the action (e.g hammer on knee) 2. Message sent along afferent nerve axon to spinal cord 3. Afferent synapses with efferent of same muscles 4. Impulse in transmitted along efferent pathway 5. Motor unit contracts (e.g. knee jerk occurs) Reciprocal Inhibition: - when one agonist muscle contracts, antagonist muscle is simultaneously inhibited Provides constant adjustment Polysynaptic Reflexes • One of more interneurons lie between primary sensory fibres and motor neurons • Increased complexity and slower • e.g. withdrawal reflex – From pain – Sensory neuron to interneuron to motor neuron Homework: From last nights reading, 1. Outline the sequence the Polynaptic Cross-Extensor Reflex 2. Complete exercise 6.6 and be ready to discuss tomorrow