Nervous System Need to Know

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Regions of the brain

Cerebrum - temporal, parietal, occipital, frontal lobes
Cerebellum - cauliflower responsible for proprioception
Diencephalon - hypothalamus (homeostatic control and neuroendocrine coupling) and thalamus (direction of sensory information to cerebral cortex)
Brainstem - mescenphalon (hearing and sight), pons (inspiration), medulla oblongata (cardiovascular and respiratory centre)

Receptors for general senses

Nociceptors: pain and itch
Thermoreceptors: temperature
Chemoreceptors: chemicals, e.g. CO2 concentration
Mechanoreceptors: tactile, baroreceptors and proprioceptors

Ways of adaptation to a stimulus

Tonic receptors: adapt slowly, always active
Phasic receptors: rapidly adapting, switch off after a while

Somatosensory pathway

Somatosensory pathways are for the direction of information from general senses to the somatosensory cortex in the cerebrum. There are three pathways:
  • Spinothalamic pathway (anterior and lateral) delivers poorly localised information regarding touch, pressure, pain and temperature to the cerebral cortex (3 neurons)
  • Posterior column pathway delivers highly localised information regarding touch, pressure, vibration and proprioception to the cerebral cortex (3 neurons)
  • Spinocerebellar pathway delivers information regarding proprioception to the cerebellar cortex (2 neurons)
When three neurons are involved: the primary neuron fires from the sensory receptor and synapses with the secondary neuron after information travels through the dorsal root and crosses the midline of the spinal cord. The secondary neuron fires up the spinal cord and synapses with the tertiary neuron, which is directed to a specific area of the somatosensory cortex by the thalamus.

When two neurons are involved, there is no tertiary neuron and the secondary neuron carries information from the spinal cord to the cerebellar cortex.

Somatic Nervous System

The somatic nervous system is the motor nervous system of which we are conscious and can control to a certain extent. An upper neuron from the cerebral cortex (primary motor cortex) descends down into the spinal cord and synapses with a lower neuron at the level in the spinal cord that the lower neuron will exit via the ventral root. The lower neuron carries the neural impulse to the effector tissue and released acetylcholine. The somatic nervous system is always stimulatory.

Autonomic Nervous System

The autonomic nervous system is completely involuntary and is divided into two systems: sympathetic and parasympathetic. It can be either stimulatory or inhibitory.

The sympathetic nervous system has the following characteristics:
  • Uses energy
  • Neurons of thoracic and lumbar origin
  • Short preganglionic fibres, long postganglionic fibres
  • Preganglionic fibres release acetylcholine onto cholinergic receptors
  • Postganglionic fibres release norepinephrine onto adrenergic receptors or adrenaline onto receptors for sweat glands
The parasympathetic nervous system has the following characteristics:
  • Produces energy
  • Digestion
  • Neurons of sacral and cervical origin
  • Long preganglionic fibres, short postganglionic fibres
  • Preganglionic fibres release acetylcholine onto cholinergic receptors
  • Postganglionic fibres release acetylcholine onto cholinergic receptors

Tonic control, dual innervation and autonomic tone

Tonic control: one signal is always present and it is increase/decrease in the signal that controls activity, e.g. blood vessel diameter

Dual innervation: instructions are given from both divisions of the autonomic system that oppose each other

Autonomic tone: there is always a resting (basal) level of spontaneous activity

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