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๐Ÿ“– Summaries โ€บ Zoology

Neural Control and Coordination

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Neural Control and Coordination

The neural system and the endocrine system jointly coordinate and integrate all activities of the organs so that they function in a synchronised fashion. The neural system provides an organised network of point-to-point connections for quick coordination, while the endocrine system provides chemical integration through hormones.

Human neural system

Divided into two parts:
  • Central neural system (CNS): brain and spinal cord; site of information processing and control.
  • Peripheral neural system (PNS): all nerves associated with the CNS.
- Afferent fibres: carry impulses from tissues/organs to the CNS. - Efferent fibres: carry regulatory impulses from the CNS to tissues/organs. - PNS has two divisions: somatic (to skeletal muscles) and autonomic (to involuntary organs and smooth muscles). The autonomic system is further classified into sympathetic and parasympathetic.

Neuron

Three major parts: cell body (with Nissl's granules), dendrites (carry impulses towards cell body) and axon (carry impulses away). Axon terminals end in synaptic knobs with synaptic vesicles containing neurotransmitters.
  • Types by number of axons/dendrites: multipolar (cerebral cortex), bipolar (retina), unipolar (embryonic stage).
  • Axons: myelinated (Schwann cells form a myelin sheath; gaps are nodes of Ranvier; in spinal and cranial nerves) and unmyelinated (no sheath; in autonomic and somatic systems).

Nerve impulse

  • Resting potential: at rest the membrane is more permeable to K+ and nearly impermeable to Na+. Na-K pump moves 3 Na+ out for 2 K+ in. Outer surface positive, inner negative (polarised).
  • Action potential: a stimulus makes the membrane freely permeable to Na+; rapid Na+ influx reverses polarity (depolarisation). This action potential is the nerve impulse. The impulse spreads along the axon; rising K+ permeability and K+ efflux restore the resting potential.

Synapse

Junction between a pre-synaptic and a post-synaptic neuron. Two types:
  • Electrical synapse: membranes very close; current flows directly; faster than chemical; rare in our system.
  • Chemical synapse: separated by a synaptic cleft; uses neurotransmitters. Impulse causes vesicles to fuse and release neurotransmitters, which bind receptors on the post-synaptic membrane, opening ion channels and generating a new potential that may be excitatory or inhibitory.

Brain (Central Neural System)

Covered by cranial meninges: dura mater (outer), arachnoid (middle), pia mater (inner). Three major parts:
  • Forebrain: cerebrum, thalamus, hypothalamus. Cerebrum has two hemispheres joined by the corpus callosum; cortex = grey matter (cell bodies), inner = white matter (myelinated tracts). Thalamus = sensory and motor coordinating centre. Hypothalamus controls temperature, hunger and thirst and secretes hypothalamic hormones. The limbic system regulates emotions, sexual behaviour and motivation.
  • Midbrain: between thalamus/hypothalamus and pons; has the cerebral aqueduct and corpora quadrigemina (four dorsal lobes).
  • Hindbrain: pons (fibre tracts), cerebellum (convoluted surface, coordination/balance) and medulla (controls respiration, cardiovascular reflexes and gastric secretions).
  • Brain stem = midbrain + pons + medulla oblongata; connects brain and spinal cord.