SSS 2: Nervous Co-ordination (I)

                      Nervous system

                            Co-ordination 

Co-ordination is defined as the process by which different parts of an organism work together for proper effectiveness.

Coordination is achieved in the body of mammals through the action of: 

1. The nervous system

2. The endocrine system (Hormones)

The hypothalamus of the brain is the link between the two systems.

Hormones - They are chemical substances secreted by endocrine (ductless) glands, directly into the blood (circulatory system) which on reaching a target organ, stimulate the activity of that organ.

Hormonal	Nervous
Transmission is chemical	Transmission is mechanical  and chemical
Slow transmission	Rapid transmission
The response is widespread	Response is localized
Target organs receive response	effector organs receive response
Long last response	short-lived response
the pathway is not specific through blood	pathway is specific through nerve fibers

Actions are involuntary	Actions are voluntary and  involuntary
It occurs in plants and animals	it occurs only in animals

            Nervous system in mammals 

The nervous system is made up of two parts:

1. Central nervous system (CNS)

2. Peripheral nervous system (PNS)

         

Central nervous system (CNS)

The central nervous system is made up of;

A.  The Brain 

B.  The Spinal cord 

                (A)     THE BRAIN

The brain is an organ made up of a large mass of nerve tissue protected within the skull or cranium.

      Dorsal view of the brain of Rabbit 

                Parts of the brain

The  main parts of the human brain are:

(a) The forebrain

(b) The midbrain

(c) The hindbrain 

                      The forebrain 

The forebrain is made up of two main parts:

(I) Cerebrum 

(II) Olfactory lobes 

It is also made up of two minor parts:

(I) Thalamus 

(II) Hypothalamus

                          Cerebrum  

I. The cerebrum is the largest part of the brain.

II.  It is made up of right and left hemispheres which are partially separated by a deep furrow called median fissure.

III.  It is protected by a band of fibers called the corpus callosum.

IV.  Each cerebral hemisphere is divided into four lobes: 

•frontal lobes

•temporal lobes

•parietal lobes

•occipital lobes 

V. The outer part of the cerebrum is called the cerebral cortex. It is made up of grey matter. The grey matter is a result of the colour of its unsheathed nerve cells.

VI. The inner part of the cerebrum is called the white matter. The white matter is a result of the white color of the sheath nerve cells.

VII. The body of the cerebrum is rough and in folds or convolution which provides a large surface area

           Functions of the cerebrum

I. The cerebrum controls all voluntary actions e.g. Speech, walking, eating, jumping, running, reading, learning, etc

I. The cerebrum is the seat of consciousness and senses. 

II.  It is also involved in the following: intelligence, memory, judgment, learning, imagination, emotion, etc. 

 IV. It collects and stores information.

                      Olfactory lobes 

They are located anteriorly at the forebrain. 

They are a pair of small structures.

They are connected with smell.

Function: They receive sensory impulses of smell

                        Thalamus 

The thalamus (singular: thalami) has two ovoid structures attached to the back of the forebrain.

               Functions of thalamus

I. It helps in experiencing sensation 

II. It is the seat of consciousness 

III. It receives impulses from the midbrain, hindbrain, and spinal cord.

IV. It sends impulses to the cerebral cortex and vice versa

                   Hypothalamus 

The hypothalamus is located just below the thalamus. It plays an important role in homeostasis. It is the main coordinating and control center for the autonomic nervous system.

            Functions of hypothalamus

(a) connects the pituitary gland or master gland to the thalamus

(b) It contains the reflex centers

(c) It regulates body temperature.

(d) It regulates water balance and osmoregulation.

(e) I control sleep and wakefulness.

(f) It controls blood flow

(g) It is the seat of aggression and anger

(h) It is the center for appetite and feeding (i) It controls the pituitary gland.

(j) It controls speech 

(k) It controls pressure 

                            The Midbrain 

The midbrain consists of a small and inconspicuous part of the brain. It is a very short region consisting of optic lobes, pineal body, and pituitary gland.

                 Functions of midbrain

1. The optic lobes receive sensory impulses from the eye. It is the site of the vision 

2. It connects the forebrain to the hindbrain thereby helping in transmitting impulses.

                       The Hindbrain 

The hindbrain together with the midbrain helps in coordinating most of the body's automatic involuntary activities.

The hindbrain is composed of the cerebellum, pons varolii, and medulla oblongata.

                          Cerebellum 

The cerebellum is the thick and convoluted portion of the hindbrain.

            Functions of the cerebellum 

(a) It controls the posture or balance of the body 

(b) It coordinates the various muscle actions in involuntary responses.

(c) It receives impulses from auditory organs (semi-circular canals of the ear) and skin

                  Pons Varolii 

It is a broad band of fibers that connect the lateral cerebellar hemispheres.

                  Medulla oblongata

It is the posterior end of the brain that continues into the spinal cord.

            Functions of the medulla oblongata

(a) Medulla oblongata controls breathing and respiration;

(a) It controls heart-beat

(b) It controls digestion.

(c) It controls the size of blood vessels. Thereby controlling blood pressure

(e) It controls the secretion of saliva.

(f) It controls laughing.

(g) It controls involuntary actions such as sneezing, blinking, coughing, yawning, etc.

           (B)        THE  SPINAL CORD 

The spinal cord is made up of soft tissue that runs from the medulla oblongata to the tail region. It is protected by the bones of the vertebral column but passes through the neural canal.

The spinal cord is enveloped within three membranes called Meninges.

The meninges are:

1. Pia mater 

2. Dura mater 

3. Arachnoid mater 

The meninges support and protect the spinal cord.

The spinal canal runs down the center of the spinal cord. It is filled with a fluid called cerebrospinal fluid 

 The transverse section of the spinal cord 

The transverse section of the spinal cord contains a greyish central region called the grey matter which is surrounded by a lighter region called the white matter.

The grey matter contains the cell bodies of the neurons in the spinal cord. The white matter consists of the nerve fibres of the cell bodies.

             Functions of the spinal cord 

1. It coordinates simple reflex actions e.g. Knee jerk, sweating, etc 

2. It acts as a pathway between the spinal nerves and the brain