What are the components of the somatic nervous system?
- Receptors and/or free nerve endings
- Afferent (sensory) nerve and ascending pathways
- Specific areas of CNS (e.g. somatomotor cortex)
- Efferent (descending) pathways in CNS
There is One efferent neurone in peripheral nervous system - describe it:
- Cell body in CNS
- Myelinated for rapid conduction
- Releases the neurotransmitter
Acetylcholine (ACh) - Innervates only skeletal muscle
- Always excitatory i.e. causes contraction
Signal transduction route:
Afferent nerves are involved with the reception of stimuli - what can the stimuli be?
- touch
- heat
- pain
- hearing
- sight
How is incoming information coordinated?
- coordinated by the spinal cord, somatomotor cortex, and the cerebellum to achieve skilled motor programs
What causes muscle contraction?
- Efferent nerves that transmit impulses form the CNS to the skeletal muscles
How does the somatic path work?
- Sensory receptor in skin detects flies biting for example
- Sensory (afferent) neurone conducts nerve impulse to the CNS
- Ascending neurone in CNS carry information to cerebral cortex where the information is consciously perceived
- Brain interprets and plans a response
- Nerve impulse is conducted from the upper motor neurone of the somatomotor cortex to the spinal (lower) motor neurone
- Somatic lower motor neurone carries impulses to skeletal muscles which contract
What is a reflex arc?
= neural pathway mediating a reflex action
Sensory (afferent) inputs do not go straight to the brain - what do they do instead?
what does this allow?
- synapse in spinal cord with an efferent (motor) neurone
- This allows reflex actions to occur quickly – does not rely on routing info to brain for a decision!
What does the brain receive while the reflex action occurs?
- sensory input
Why are reflexes considered somatic even through they are not voluntary?
- Reflexes that output to skeletal muscles use the same nerve pathways as somatic NS, so are considered somatic
Some reflexes are visceral (autonomic) and are therefore not somatic - give an example:
- E.g. baroreceptor reflex (blood pressure)
How do you perform the withdrawal reflex?
- Pinch toe
- Flexor muscles contract
- Limb is withdrawn
(Conscious acknowledgement)
What does testing the withdrawal reflex allow?
- Testing a reflex allows the vet to evaluate all components along that path
Combining findings from multiple tests allows vet to localise the problem and lead on to what?
- Further testing e.g. where to x-ray
- Differential diagnoses
During the withdrawal reflex what happens when the toe is pinched?
- Afferent neurone to CNS
- Ulnar, median or radial nerve (depending on where you pinch - lateral, palmar or dorsal sensory innervation)
During the withdrawal reflex what happens in the CNS?
- Synapse of afferent and efferent nerve (via interneurone)
- C6-T2 of spinal cord (brachial plexus region)
What happens when the limb is withdrawn?
- Efferent neurone to muscles (flexors of all forelimb joints)
- E.g. axillary, musculocutaneous, median, ulnar nn.
What is involved in animal acknowledgement (lick paw)?
- Ascending sensory pathways and forebrain
What do somatosensory receptors detect?
- pain, temperature, touch and body position (proprioception), so that the animal can perceive and respond
Where are Golgi tendon organs located and what do they detect?
- tendons
- stretch
Where are muscle spindles located and what do they detect?
- muscle
- stretch
Where are meisnners corpuscles located and what do they detect?
- skin
- light touch
Where are Merkel’s disks located and what do they detect?
- skin
- touch and textures
Where are pancinian corpuscle located and what do they detect?
- skin
- pain and deep pressure
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Basic Principles of Biological Communication56
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Nervous system functional anatomy77
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Somatic Nervous System26
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Autonomic nervous system74
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Brain circulation, meninges and CSF41
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Lower motor neurones52
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Sensory organs91
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Membrane Transport38
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Neurotransmission - Nerves50
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Neurotransmission 2 - synapses49
