An average adult’s brain is one of the largest organs of the human body. In brain anatomy we learn that the brain is composed of 4 main parts:
The Brainstem
The Brain Stem a.k.a. Medulla Oblongata is the primitive part of the brain. It is not related to higher intelligence, but it is important for maintaining the breathing rate, heart rate etc.
The brainstem is the part which connects the cerebrum of the brain to the spinal cord and cerebellum. The brainstem is composed of the midbrain, the pons and the medulla oblongata. It acts as a conduction pathway for motor and sensory impulses between the brain and the spinal cord. Some co-ordinations which are considered as non-vital that are also produced from the Medulla include swallowing, vomiting, coughing, sneezing and hiccuping.
Within the medulla oblongata is an area known as the Reticular Formation where there is dispersed grey matter containing white fibres (portions of the Reticular Formation are also located within the spinal cord, pons, midbrain and diencephalon). This area is responsible for consciousness and arousal.
The Reticular Formation has 3 vital reflex centres, namely the Cardiac Centre, which regulates the heartbeat and force of contraction; the Medullary Rhythmicity Area, which adjusts the basic breathing rhythm; and the Vasomotor Centre, which regulates the blood vessels’ diameter.
The Diencephalon
The Diencephalon is a rather hidden small structure within the brain which can be found just above the brainstem, right between the cerebral hemispheres. It houses the epithalamus, thalamus, subthalamus and hypothalamus.
The Thalamus consists of two oval masses made of mostly grey matter which is organised into Nuclei forming the lateral walls of the third ventricle. Additionally the thalamus acts as an interpretation centre for some sensory impulses, such as pain, temperature, light touch and pressure. Certain nuclei within the thalamus serve as relay stations for all sensory impulses (other than smell) to the cerebral cortex. Other nuclei are centres for synapses in the somatic motor system.
The Hypothalamus, which is partially protected by the cella turcica of the sphenoid bone, is a small portion of the diencephalon, forming the floor and part of the lateral walls of the third ventricle. Afferent pathways originating in the peripheral sense organs make way for information from the external environment in relation to sound, taste, smell and somatic sensations, to travel to the hypothalamus. Similarly, it is also associated with feelings of rage and aggression; it regulates food intake through the feeding centre and the satiety centre, and maintains the waking state and sleep patterns.
The hypothalamus is also responsible for the monitoring of water level, hormone concentrations and blood temperature. Additionally, the hypothalamus is the principal intermediary between the nervous system and the endocrine system, releasing chemicals called regulating factors following body changes, leading to the stimulation or the inhibition of the anterior pituitary gland. Two particular hormones which are produced by the hypothalamus are the Antidiuretic Hormone (ADH) and Oxytocin.
The hypothalamus controls and integrates the autonomic nervous system by stimulating smooth muscle, regulating the cardiac muscle contraction rate as well as the secretion of many glands.
The Cerebrum
The Cerebrum makes up the largest part of the brain. It is involved in reasoning, personality, emotional intelligence, sensory, and motor functions.
The Cerebrum – the front part of the brain which comprises of gray matter (peripheral cerebral cortex) and white matter within its centre. It occupies most of the cranium space and comprises of around 7/8 of the total brain weight. The cerebrum houses a number of nuclei, including the basal ganglia, the thalamus and the hypothalamus.
The basal ganglia are paired masses of grey matter found within each cerebral hemisphere, interconnected by many fibres, and also connected to the cerebral cortex, thalamus and hypothalamus.
The caudate nucleus and the putamen control large subconscious movements of the skeletal muscles, such as arm swinging whilst walking. Gross movements are also consciously controlled by the cerebral cortex.
The globus pallidus is associated with the regulation of the muscle tone required for specific body movements.
The cerebral cortex is divided into the Sensory Areas, which interpret sensory impulses; the Motor Areas, which control muscular movement; and Association Areas, which are related to emotional and intellectual processes.
The Cerebellum
The Cerebellum is involved in fine movements.
The Cerebellum – a structure located at the back of the brain which lies inferior to the cerebrum and posterior to the brainstem. It is a motor area of the brain which is concerned with certain subconscious movements in the skeletal muscles – muscles which are required for the provision of postural adjustments for balance maintenance.
Motor areas of the cerebral cortex are able to initiate muscle contraction voluntarily. During movement, sensory areas of the cortex receive impulses from the joint nerves, which point to the extent of muscle contraction and joint movement. This action is referred to as proprioception. Proprioception determines which muscles need to contract and the strength of contraction required. The cerebral cortex then generates impulses to the pons and midbrain, which then relay the impulses over the middle and superior cerebellar peduncles to the cerebellum. A very short delay then occurs to allow the coordination of muscle contractions sequence.
The Limbic System
BRAIN ANATOMY – PROTECTION
The brain is protected by 8 cranial bones and the meninges…
Cranial Bones
Meninges
The meninges are made up of 3 main layers, namely the Dura Mater (outer layer), the Arachnoid (middle layer), and the Pia Mater (inner layer). Between the Arachnoid Mater and the Pia Mater is the Subarachnoid Space, which contains Cerebrospinal Fluid (CSF) that provides protection, as well as cleans and nourishes the brain.
CSF Flow
The CSF circulates through the subarachnoid space around the brain and spinal cord as well as through the brain’s ventricles…
Brain Anatomy – Ventricles
There are 4 cavities within the brain:
- 2 Lateral Ventricles
- Third Ventricle
- Fourth Ventricle
Brain Anatomy – Blood Supply
The brain utilises approximately 20% of the entire body’s oxygen supply. The Cerebral Arterial Circle is a collection of blood vessels that supply the brain with oxygen, glucose and nutrients.
Since the brain’s capacity for carbohydrate storage is limited, continuous glucose supply is a must.
Cerebral blood flow depends on Carbon Dioxide and Oxygen supply.
Functions of the Main Parts of the Brain
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