6. Divisions of the Nervous System

Ganglion

Group of cell bodies, outside of the brain and spinal cord

Cranial Nerves

• 12 Pairs

• Sensory fibres carry impulse to the CNS

• Motor fibres carry impulse away from the CNS

• Most cranial nerves are mixed

Spinal Nerves

31 Pairs

All mixed nerves (sensory and motor) joined to the spinal cord by:

• Ventral roots containing motor neurons with cell bodies in the grey matter of the spinal cord

• Dorsal roots containing sensory neurons with cell bodies in the swelling (Dorsal ganglion)

Nervous System - Divisions

CNS → Brain or Spinal Cord

PNS → Sensory Division (→ Somatic Sensory or Visceral Sensory) → or Motor Division (→ Somatic Motor or Autonomic Motor (→ Sympathetic or Parasympathetic)

Autonomic Nervous System

• Responsible for homeostasis

• Involuntary control (unconscious)

• Regulated by the Medulla oblongata, hypothalamus, and cerebellum

Autonomic Nervous System - Functions

• Release of energy

• Pupil diameter

• Heart Rate

• Blood Pressure

• Body Temperature

• Digestion

• Ventilation

• Defecation & Urination

Compare somatic and autonomic

Somatic:

• Only one set of motor nerve fibres

• Neurotransmitter from neuron to muscle is acetylcholine

Autonomic:

• Two sets of motor nerve fibres (sympathetic and parasympathetic)

• Neurotransmitter from neuron to effector is either acetylcholine (parasympathetic) or noradrenaline (sympathetic)

Sympathetic - How it Affects Structures

• Sweat Glands → Increases Sweat Secretion

• Liver → Increased breakdown of glycogen to glucose

• Lungs → Dilation of bronchioles

• Stomach, intestines → Decreases Movement

• Salivary Glands → Decreases saliva secretion

• Heart → Increases heart rate

• Blood vessels (skin) → Vasoconstriction

Parasympathetic - How it Affects Structures

• Sweat Glands → No Effect

• Liver → Increased uptake of glucose and synthesis of glycogen

• Lungs → Constriction of bronchioles

• Stomach, intestines → Increases Movement

• Salivary Glands → Increases saliva secretion

• Heart → Decreases heart rate

• Blood vessels (skin) → Vasodilation

“Flight or Fight Response”

• Involves the sympathetic nervous system

• Circulatory system diverts oxygen - rich blood from digestive system towards brain and skeletal muscles

• Liver releases sugar to make more energy available

• Adrenalin increases heart rate

• Pupils dilate to let

Differences - Hormonal vs Nervous System

Nervous System:

• More rapid response (nerve impulse takes milliseconds)

• Nervous system response stops immediately once stimulus has ceased

• Nervous system involves an electrochemical change

• Nerve impulses travel to a specific part of the body

Hormonal System:

• Slower response (blood stream takes seconds to days)

• Hormonal responses are slower acting and can last for years

• Hormonal involves chemicals (hormones)

• Hormones travel to all parts of the body and can affect a number of organs

Similarities - Hormonal vs Nervous System

• Some substances act as both neurotransmitters and hormones (e.g. noradrenaline, ADH, and dopamine)

• Some neurotransmitters and hormones have the same effect on target cells e.g. noradrenaline and the hormone glucagon both act on the liver, causing it to break down glycogen into glucose (release energy)

• Some hormones are ecreted by neurons into the extracellular fluid (e.g. oxytocin and adrenaline)