The Nervous System

Published on 15th June 2018

FUNCTION

  • To transmit information  
  • To receive and respond to stimuli
  • Maintain homeostasis 

ANATOMY

There are 3 divisions:

 
Central Nervous System:

 

  • Brain 
  • Spinal cord 

Peripheral Nervous System: 

  • Cranial nerves 
  • Spinal nerves 

Autonomic Nervous System:

  • Sympathetic branch 
  • Parasympathetic branch 

THE NEURON

  • Basic unit of nervous system 
  • Combine to form nerves 
  • 3 types:  
    • Sensory - afferent 
    • Connectors 
    • Motor – efferent 
  • Impulses travel in one direction 
  • Synapse is a junction between two neurones 
  • Neuro-transmitters – Chemicals produced by axon terminals to enable or inhibit a nerve impulse to travel across synapse 
  • Myelin Sheath – Fatty insulating coating on some neurons 
  • Nodes of Ranvier – Indentations in myelin sheath at certain points 
  • Neurilemma- Fine membrane covering myelin sheath 

 

THE CENTRAL NERVOUS SYSTEM

The whole of the CNS is covered by the Meninges.  Three layers make up this covering: 

  • Dura Mater – outer layer 
  • Arachnoid Mater – middle layer 
  • BRAIN STEM Pia Mater – inner layer attached to the brain and spinal cord 

Cerebrospinal fluid is found between the arachnoid and pia mater. 

CEREBRUM

  • Divided into hemispheres and lobes 
  • Responsible for thinking, speech, learning, intellectual processes, memory 
  • Receives and interprets sensory information 
  • Controls voluntary movement

Located in the Cerebrum is the hypothalamus – an important 
regulatory area of the brain which: 

  • Controls the pituitary gland 
  • Controls the autonomic nervous system 
  • Regulates body temperature 
  • Controls hunger and thirst 
  • Controls certain emotions 
  • Regulates certain body rhythms and cycles

CEREBELLUM

Controls muscular co-ordination, balance and posture

BRAIN STEM

This is made up of: 

  • Mid Brain – acts as a relay station between different parts of brain and spinal cord 
  • Pons Varoli – connects the left and right sides of the cerebellum and helps regulate breathing 
  • Medulla Oblongata - Links cerebrum with spinal cord and is the centre of automatic activities such as breathing, heart beat, swallowing, vomiting and coughing 

SPINAL CORD

  • Runs down vertebral canal 
  • Receives sensory information and conveys it up to brain 
  • Conducts motor impulses from brain 
  • Enables reflex actions to occur 

THE PERIPHERAL NERVOUS SYSTEM

 Carries 2-way information: 

  • Sensory  from body to brain 
  • Motor  from brain and spinal cord to body 

SPINAL NERVES

  • 31 pairs 
  • Emerge from spinal cord

CRANIAL NERVES

  • 12 pairs 
  • Emerge from base of brain 

THE AUTONOMIC NERVOUS SYSTEM

  • Carries impulses to: 
    • Smooth muscle 
    • Glands 
    • Cardiac muscle 
  • Controlled and co-ordinated by hypothalamus of brain

SYMPATHETIC

  • Supplies thoracic, abdominal/pelvic organs and blood vessels and sweat glands 
  • Increases body activity mainly

PARASYMPATHETIC

  • Supplies thoracic, abdominal/pelvic organs and some cranial nerves 
  • Controls digestion 
  • Concerned mainly with conservation of energy

Sensory (afferent) Neurons

have specialised endings called receptors which pick up and carry information to the brain and respond to changes inside and outside the body: 
SKIN receptors detect :  Pain,  temperature,  touch    
TENDONS MUSCLES JOINTS  receptors detect : Stretch, movement    
SPECIAL SENSE ORGANS receptors detect :   Sight,  sound, smell, taste    
OTHER ORGANS AND GLANDS  Regulate activities such as: Breathing, heart rate,  digestion 

Motor (efferent) Neurons

are found in brain and travel to effectors to stimulate a response in : 
 

  • MUSCLES 
  • GLANDS

 

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