BYA7 SECTION 16.10Patterns Of Behaviour Are Integrated And Controlled
By The Nervous System |
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Spinal Reflexes |
- Stimuli: Change in internal or external environment
- Reflexes → automatic, same, fixed response to a stimulus
- Dilating of pupils in dim light
- Salvia production when tasting food
- Withdrawing part of your body from a painful stimulus
- Spinal reflex/Reflex arc is the nervous pathway of a reflex
- Reflex arc involves spinal cord rather than brain (quicker action)
- May involve brain
- Control of muscles in iris
- Tension in suspensory ligaments of eye
- In-born but can be adapted through learning
- Relay neurones carry impulses from reflex arc up ascending tracts in white
matter to the brain
- New relay neurones form in brain that stimulate motor neurone
- They control e.g. muscles that control speech
- Rapid and autonomic action
- Large number of receptors, sensory, relay and motor neurones involved
- Human spinal cord is a hollow tube of nervous tissue
- 31 pairs of spinal nerves enter and leave spinal cord
- Grey matter contains unmyelinated neurones (responsible for grey colour)
- Synapse of relay neurone with sensory and motor neurone
- White matter contains myelinated neurones (appear white)
- Motor and sensory neurones
- Is made up of interneuronal axons (tracts)
- Sensory neurones enter spinal cord via dorsal root (back)
- Their cell bodies are in the dorsal root ganglion
- Motor neurones leave the spinal cord via the ventral root (front)
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The Pathway and Adaptive Value of a Simple Spinal Reflex Involving 3 Neurones |
- Stimulus causes receptor to generate nerve impulse along SENSORY NEURONE
- Moves along dendrite, dorsal root, to the cell body
- Cell body is in the dorsal root ganglion, outside the cord/CNS
- From cell body along axon
- RELAY NEURONE in grey matter synapses with sensory and motor neurone
- Impulse leaves spinal cord by ventral root of the spinal nerve
- Moves along axon of MOTOR NEURONE to an effector
- E.g. release neurotransmitter into muscle cell → contract
- Brain receives information concerning sensory stimuli by other relay neurones
- Their long fibres run through ascending (to brain) and descending tracts in
the white matter of the spinal cord
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Autonomic Nervous System (ANS)
Outline of the Functions of Parasympathetic and Sympathetic Divisions of the ANS |
Table 16-10-1: The ANS controls internal glands + muscles beyond conscious control
Target Organ/Tissue
Effect on organ:
Motor neurone releases: |
Parasympathetic Stimulation
Inhibitory effect / relaxation
Acetylcholine (ACh) |
Sympathetic Stimulation
Excitatory effect / stress
Norepinephrine (noradrenlaine) |
| Iris of eyes |
Constricts pupil |
Dilates pupil |
| Bronchi, bronchioles |
Constricts tubes |
Dilates tubes |
| Blood vessels |
- Dilates blood vessel
- Lowers blood pressure |
- Constricts blood vessels
- Raises blood pressure |
| Heart |
- Lowers heart rate
- Lowers stroke volume |
- Raises heart rate
- Raises stroke volume |
| Intercostal muscles |
Lowers breathing rate |
Raises breathing rate |
| Salivary glands |
Stimulates secretion of salvia |
Inhibits secretion of salvia |
| Gut |
Stimulates peristalsis |
Inhibits peristalsis |
| Sweat glands |
No effect |
Increases sweat production |
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Specific Physiology in the Context of the Control of Heart Rate |
- Heart rate is controlled by cardiac centre in MEDULLA
- Cardio accelerator centre CAC RAISES heart rate
- Sympathetic neurones run from CAC down descending tracts
- Along spinal nerve to sinoatrial node SAN
- Release NORADRENALINE onto target cells
- Cardio inhibitor centre CIC LOWERS heart rate
- Parasympathetic neurones from CIC leave brain via VAGUS NERVE
- Releases ACETYLCHOLINE onto target cells
- CAC and CIC are always active, alter rate of depolarisation
of SAN
- Autonomic nervous system controls rate of heart contraction
- Contracting muscles pressing on veins force blood towards heart causing greater filling of the
ventricles which makes the heart beat faster and stronger
- If blood pressure rises too far above normal, pressure receptors in the aorta and carotid (artery)
sinus send nerve impulses to the CIC
- CIC send inhibitory nerve impulses to the CAC and the SAN
- Heart is myogenic, heart beats are initiated by electrical activity in the SAN, followed by the
atrioventricular node and atrioventricular bundle
- BETA BLOCKERS: bind to receptors in myocardium / prevent epinephrine (adrenaline) from binding to
the myocardium / reduce rate of contractions
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References and Further Reading
AQA (2006) GCE Biology/Biology (Human) 2006 specification, [PDF]
