Monday, August 10, 2020

Neural Control and Coordination - Notes | Class 11 | Part 3: Human Neural System - CNS

21. NEURAL CONTROL AND CO-ORDINATION

HUMAN NERVOUS (NEURAL) SYSTEM


It has 2 parts:
  1. Central neural system (CNS): Brain & spinal cord.
  2. Peripheral nervous system (PNS): All nerves.

CENTRAL NEURAL SYSTEM (CNS)


A. BRAIN
It is protected in cranial cavity.

It has 3-layered connective tissue membranes called cranial meninges.

Meninges consist of outer dura mater, middle arachnoid mater and inner pia mater.

The subarachnoid space (space between pia mater and arachnoid mater) is filled with cerebrospinal fluid (CSF). The ventricles of brain are also filled with CSF.

Brain has 3 divisions: Forebrain, Midbrain & Hindbrain.


a. Forebrain (Prosencephalon) 

It is the anterior part. Consists of cerebrum & diencephalon.

Cerebrum
Largest part. 

It has 2 cerebral hemispheres held together by a tract of nerve fibres (Corpus callosum).

Outer part of cerebrum is called cerebral cortex. It has convulsions & depressions and is formed of gray matter. Gray colour is due to the presence of neuron cell bodies.

Inner part of cerebrum is formed of white matter.

Cerebral cortex consists of
  • Motor area: Controls voluntary movements of muscles.
  • Sensory (Somaesthetic) area: Controls the functioning of sense organs.
  • Association area: It is neither clearly sensory nor motor in function. Responsible for intersensory associations, memory and communication.
Integrated activities of different centres of cerebral cortex control intelligence, memory, judgment, learning, thinking and articulate speech. 

Diencephalon (Thalamus & Hypothalamus) 

⇒ Thalamus: 
  • It is the structure around which the cerebrum wraps. 
  • It is a coordinating centre (relay station) for sensory and motor impulses. 
⇒ Hypothalamus: 

Seen below the thalamus. It
  • Regulates temperature, thirst, hunger and emotions.
  • Secretes hypothalamic hormones.
  • Controls pituitary gland.
  • Controls sleep, wakefulness, blood pressure, heart rate.
The inner parts of cerebral hemispheres and a group of associated deep structures like amygdala, hippocampus, hypothalamus, etc. together constitute Limbic system (Limbic lobe). It regulates sexual behavior, motivations, emotions (excitement, pleasure, rage, fear etc).

b. Midbrain (Mesencephalon) 
  • It is located between thalamus/hypothalamus and Pons.
  • A canal (cerebral aqueduct) passes through the mid brain.
  • Mid brain consists of 4 round lobes called Corpora quadrigemina. Their anterior pair is the centre of visual reflexes and the posterior pair is a centre of auditory reflex.
c. Hindbrain (Rhombencephalon) 

It consists of cerebellum, Pons & Medulla oblongata. 

Midbrain & hindbrain form the Brain stem.

⇒ Cerebellum (“little cerebrum”): 
  • It has very convoluted surface to accommodate more neurons. 
  • It co-ordinates muscular activities and body equilibrium. 
⇒ Pons varoli: 
  • It consists of fibre tracts that interconnect different regions of the brain. 
  • It co-ordinates the activities of eye and ear and regulates respiration. 
⇒ Medulla oblongata: 
  • It is connected to spinal cord. 
  • It controls respiration, cardiovascular reflexes, gastric secretions, peristalsis etc. 
  • It also controls salivation, vomiting, sneezing & coughing. 
B. SPINAL CORD 
  • It is enclosed within the spinal canal of vertebral column.
  • It is also protected by meninges.
  • Spinal cord has a central canal containing CSF.
  • Outer white matter and inner gray matter.
Functions:
  • Conduction of impulses to and from the brain.
  • Centre of spinal reflexes.
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