Anatomy and physiology of the brain and spinal cord
The brain is a spongy organ made up of nerve and supportive tissues. It is located in the head and is protected by a bony covering called the skull. The base, or lower part, of the brain is connected to the spinal cord. Together, the brain and spinal cord are known as the central nervous system (CNS). The spinal cord contains nerves that send information to and from the brain.
The CNS works with the peripheral nervous system (PNS). The PNS is made up of nerves that branch out from the spinal cord to relay messages from the brain to different parts of the body. Together, the CNS and PNS allow a person to walk, talk, throw a ball and so on.
Structure and function of the brain
The brain is the body’s control centre. It constantly receives and interprets nerve signals from the body and responds based on this information. Different parts of the brain control movement, speech, emotions, consciousness and internal body functions, such as heart rate, breathing and body temperature.
The brain has 3 main parts: cerebrum, cerebellum and brain stem.
The cerebrum is the largest part of the brain. It is divided into 2 parts (halves) called the left and right cerebral hemispheres. The 2 hemispheres are connected by a bridge of nerve fibres called the corpus callosum.
The right half of the cerebrum (right hemisphere) controls the left side of the body. The left half of the cerebrum (left hemisphere) controls the right side of the body.
The outer surface of the cerebrum is called the cerebral cortex or grey matter. It is the area of the brain where nerve cells make connections, called synapses, that control brain activity. The inner area of the cerebrum contains the insulated (myelinated) bodies of the nerve cells (axons) that relay information between the brain and spinal cord. This inner area is called the white matter because the insulation around the axons gives it a whitish appearance.
The cerebrum is further divided into 4 sections called lobes. These include the frontal (front), parietal (top), temporal (side) and occipital (back) lobes.
Each lobe has different functions:
- The frontal lobe controls movement, speech, behaviour, memory, emotions and intellectual functioning, such as thought processes, reasoning, problem solving, decision making and planning.
- The parietal lobe controls sensations, such as touch, pressure, pain and temperature. It also controls spatial orientation (understanding of size, shape and direction).
- The temporal lobe controls hearing, memory and emotions. The left temporal lobe also controls speech.
- The occipital lobe controls vision.
The cerebellum is the next largest part of the brain. It is located under the cerebrum at the back of the brain. It is divided into 2 parts or hemispheres and has grey and white matter, much like the cerebrum.
The cerebellum is responsible for:
- complex actions (walking, talking)
- collecting sensory information from the body
The brain stem is a bundle of nerve tissue at the base of the brain. It connects the cerebrum to the spinal cord and sends messages between different parts of the body and the brain.
The brain stem has 3 areas:
- medulla oblongata
The brain stem controls:
- body temperature
- blood pressure
- heart rate
- hunger and thirst
Cranial nerves emerge from the brainstem. These nerves control facial sensation, eye movement, hearing, swallowing, taste and speech.
Other important parts of the brain
Cerebrospinal fluid (CSF)
The cerebrospinal fluid (CSF) is a clear, watery liquid that surrounds, cushions and protects the brain and spinal cord. The CSF also carries nutrients from the blood to, and removes waste products from, the brain. It circulates through chambers called ventricles and over the surface of the brain and spinal cord. The brain controls the level of CSF in the body.
The brain and spinal cord are covered and protected by 3 thin layers of tissue (membranes) called the meninges:
- dura mater – thickest outer layer
- arachnoid layer – middle, thin membrane
- pia mater – inner, thin membrane
CSF flows in the space between the arachnoid layer and the pia mater. This space is called the subarachnoid space.
The tentorium is a flap made of a fold in the meninges. It separates the cerebrum from the cerebellum.
- The supratentorial area of the brain is the area above the tentorium. It contains the cerebrum, the first and second (lateral) ventricles, the third ventricle, and glands and structures in the centre of the brain.
- The infratentorial area is located at the back of the brain below the tentorium. It contains the cerebellum and brain stem. This area is also called the posterior fossa.
The corpus callosum is a bundle of nerve fibres between the 2 cerebral hemispheres. It connects and allows communication between both hemispheres.
The thalamus is a structure in the middle of the brain that has 2 lobes or sections. It acts as a relay station for almost all information that comes and goes between the brain and the rest of the nervous system in the body.
The hypothalamus is a small structure in the middle of the brain below the thalamus. It plays a part in controlling body temperature, hormonehormoneA substance that regulates specific body functions, such as metabolism, growth and reproduction. secretion, blood pressure, emotions, appetite, and sleep patterns.
The pituitary gland is a small, pea-sized organ in the centre of the brain. It is attached to the hypothalamus and makes a number of different hormones that affect other glands of the body’s endocrine systemendocrine systemThe group of glands and cells in the body that make and release hormones (which control many functions such as growth, reproduction, sleep, hunger and metabolism) into the blood.. It receives messages from the hypothalamus and releases hormones that control the thyroid and adrenal gland, as well as growth and physical and sexual development.
The ventricles are fluid-filled spaces (cavities) within the brain. There are 4 ventricles:
- The first and second ventricles are in the cerebral hemispheres. They are called lateral ventricles.
- The third ventricle is in the centre of the brain, surrounded by the thalamus and hypothalamus.
- The fourth ventricle is at the back of the brain between the brain stem and the cerebellum.
The ventricles are connected to each other by a series of tubes. The fluid in the ventricles is cerebrospinal fluid (CSF). The CSF flows through the ventricles, around the brain in the space between the layers of the meninges (subarachnoid space) and down the spinal cord.
The pineal gland is a very small gland in the third ventricle of the brain. It produces the hormone melatonin, which influences sleeping and waking patterns and sexual development.
The choroid plexus is a small organ in the ventricles that makes CSF.
There are 12 pairs of cranial nerves that perform specific functions in the head and neck area. The first pair starts in the cerebrum, while the other 11 pairs start in the brain stem. Cranial nerves are indicated by number (Roman numeral) or name.
vision and light detection by the pupil
eye movement upward, downward or inward
narrowing and widening of the pupil
lifting of the eyelid
eye movement downward and inward
outward eye movement
closing of the eyelid
taste in the front part of the tongue
speech (vocal cords)
control of muscles in internal organs
The blood-brain barrier is a specialized system of blood vessels and enzymesenzymesA protein that speeds up certain chemical reactions in the body. that protect the brain from chemicals or toxins produced by bacteria. It helps maintain a constant environment for the brain.
The blood-brain barrier is made up of very small blood vessels (capillaries) that are lined with thin, flat endothelial cells. In other parts of the body, endothelial cells have small spaces between them that allow substances to move in and out of the capillary so they can reach other cells and tissues. In the brain, the endothelial cells are packed tightly together so substances cannot pass out of the bloodstream into the brain. The enzymes also restrict the types of substances that can be carried from the bloodstream into the brain.
Some substances can pass through the blood-brain barrier, such as very small molecules and molecules that can be dissolved in fat (are lipid soluble).
Types of cells in the brain
The brain is made up of neurons and glial cells:
- These cells carry the signals that make the nervous system work.
- They cannot be replaced or repaired if they are damaged.
- glial cells (neuroglial cells)
- These cells support, feed and protect the neurons.
- The different types of glial cells are:
- ependymal cells
- microglial cells
Structure and function of the spine
The spine is made up of:
- vertebrae, sacrum and coccyx – bony sections that house and protect the spinal cord (commonly called the spine)
- The vertebral body is the biggest part of a vertebra. It is the front part of the vertebra, which means it faces into the body.
- spinal cord – a column of nerves inside the protective vertebrae that runs from the brain to the bottom of the spine
- disc – a layer of cartilage between each vertebra that cushions and protects the vertebrae and spinal cord
The spine is divided into 5 sections:
- cervical – the vertebrae from the base of the skull to the lowest part of the neck
- thoracic – the vertebrae from the shoulders to mid-back
- lumbar – the vertebrae from mid-back to the hips
- sacrum – the vertebrae at the base of the spine
- The vertebrae in this section are fused and do not flex.
- coccyx – the “tail bone” at the end of the spine
- The vertebrae in this section are fused and do not flex.
The spine relays messages between the body and the brain. These nerve messages control body functions like movement, bladder and bowel control and breathing. Each vertebra has a pair of spinal nerves that receive messages from the body (sensory impulses) and send messages to the body (motor impulses). The spinal nerves are numbered from the cervical spine to the sacral spine.
|Number||Part of spine||Function|
C1 to C8
send messages to the back of the head, neck, shoulders, arms, hands and diaphragm
T1 to T12
send messages to the chest, some back muscles and parts of the abdomen
L1 to L5
send messages to the lower parts of the abdomen and the back, some of the legs and some parts of the external genital organs
S1 to S5
send messages to the thighs, lower parts of the legs, feet, most of the external genital organs, the groin area, the bladder and the anal sphincter