Embryological development and divisions of nervous system
Embryonic neural tube which is a hollow structure from epithelial origin, develop into brain and spinal cord. Brain is derived from anterior portion and spinal cord is divided from posterior portion of neural tube.
Anterior portion develop into three swellings – Rombencephalon (Hind brain), Mesencephalon (Mid brain) and Prosencephalon (Fore brain).
- Cavity that develop in the centre is known as ventricles which are filled with cerebrosipinal fluid (CSF) and ependymal cells, a type of glial cell allow the circulation of CSF into ventricular and spinal cord due to their ciliary action.
- Hind brain controls reflex responses and regulate involuntary behaviour (breathing, equilibrium, maintenance of body position).
- Mid brain is predominantly involved in co-ordinating visual, auditory or sensory information from mechanoceptors (touch/pressure ) from parts of the body. It acts as a routing centre.
- Fore brain is involved in processing olfactory information, integerates with other sensory information, regulates body vegetative functions. It is designated to perform complex tasks like memory processing etc.
- Size of the brain varies with body size individual structures type of activity pertaining to the environment of the animal.
- Basal nuclei is the cluster of grey matter situated deep into the brain.
Hind brain: (Pons , Medulla and cerebellum)
Location: Between spinal cord mid brain. Functions together to support vital body functions such as respiration cardiac function and movement.
- Medulla
- Located at the top of the spinal cord
- Has centres that control reflex activities such as respiration, heart rate, vasodilation and blood pressure.
- Houses neural pathways that connects cerebral cortex and spinal cord seat of some of the cranial nerves (9th, 10th and 12th).
- Pons
- Structures present above the medulla functions as bridging and communicating informations between medulla, cerebellum and fore brain structures.
- Has neurons that control rate of respiration.
- Concerned control of alertness.
- Cerebellum
- Encased in cerebellar hemisphere and is located in the back of the brain.
- Responsible for motor co ordination by integerating sensory inputs from receptors of muscle, eyes and ears with motor orders of the forebrain.
- Maintain Equilibrium and posture.
Mid brain
- Relay centre
- Roof of midbrain is known as tectumwhich has pair of brain centres namely optic lobes in non mammalian species.
- Superior Colliculi is a similiar structure as optic lobes in mammals functions as reflex optical response (orientation towards visual stimuli, focussing etc).
- Tectum has a pair of inferior colliculi which are neurons concerned with hearing.
- Tegmentum is the posterior part of midbrain that possess fine control of muscles.
- Brain stem is the grouping of midbrain with the pons and medulla.
Fore brain
- Involved in processing and integrating sensory information and co ordinates behaviour.
- Structures of the fore brain consists of cerebrum , thalamus, epithalamus and hypothalamus.
- Cerebrum
- Has outer layer known as cerebral cortex which is divided into two cerebral hemispheres.
- Hemispheres excercise control over opposite side of the body.
- Hemispheres functions independently of each other.
- Two hemispheres are connected by a mass of white matter known as corpus collosum through which they communicate.
- Hypothalamus
- Present in the base of the forebrain, below the thalamus.
- Maintains homeostasis by controlling internal organs and interacts with autonomic nervous system.
- Regulates endocrine system and links endocrine and neural systems.
- Controls vegetative functions of the body.
- If forms the part of limbic system which influences emotion and behaviour.
- Limbic system is a network of connected structures that lie between the cortex and reset of the brain.
- Structures associated with limbic systems are hypothalamus, amygdala, hippocampus and olfactory bulbs.
- Structures of limbic system
- Amygdala
- Concerns with emotional responses of fear and aggressiveness.
- It is also involved in maintenance of memories of the emotion.
- Hippocampus
- Structures convert short term memories to long term memories.
- Olfactory bulb
- Organ of importance for sensing the smell. Behaviours are smell driven in animals. Sensory neurons from the olfactory epithelium are connected to the olfactory bulb.
- Olfactory information reaches directly here without passing through thalamus.
- Information are transmitted to cortex for processing .
- It is connected to amygdala and hippocampus. Emotional behaviours are mediated through odours in animals and human beings.
- Amygdala
- Thalamus
- Act as relay centre, largest sensory ganglion of the brain
- Has group of grey matter located deep into the forebrain.
- Receive all sensory information for upward transmission except olfaction.
- Reticular formation is a set of neurons extend from thalamus to brain stem including pons, medulla and midbrain, that filters incoming sensory information.
- Epithalamus
- Located above the thalamus harbours pineal complex, that establishes circadian rhythm and secretes melatonin.
