Characteristics that Pre-Determine a Person’s Biological Make-Up
Although a person’s behaviour is largely influenced by their environment, there are certain characteristics that are predetermined by the person’s biological make up. Some of these characteristics are common to all people (to all human beings) while others may be specific to different people.
For instance, all normal infants have a startle reflex, and all tend to be fearful of heights. Some children, however, seem to startle more easily because their neurons fire more anxiety messages. If a person’s nervous system is damaged, it might be impossible for them to name another person even though that other person is familiar to them.
These are matters investigated by neurobiological psychology, which is concerned with the relationship between the person’s biology and nervous system and their psychological make up and behaviours.
The nervous system is not completely developed upon birth, but continues to develop as the body matures, and we become capable of more complex physical and psychological activities. Maturation is the process of growth development which enables a person to learn a new form of behaviour.
Most maturation processes are complete in the human being before the age of twenty. The two periods which involve the most rapid maturational changes are the first five years of life, and puberty. In an infant, the cerebral cortex is incomplete, and the synapses that allow messages to pass from one nerve to another are not yet linked to the appropriate nerves.
Also, the axons, which are crucial in the transmission of messages between nerves, lack the myelin sheath, an insulating sheath that allows for much more rapid transmission of messages. The lack of the myelin sheath prevents the infant from controlling the lower parts of its body. Myelination and development of synapses continues into adolescence, and perhaps even into adult hood.
STRUCTURES OF THE NERVOUS SYSTEM
The nervous system is rather like the look-out on a river boat: it monitors conditions, keeps the boat on
course, and gives warnings when something unusual or dangerous is ahead. The nervous system allows
humans to adapt to changes that can occur within the body (such as oxygen depletion after strenuous
exercise) or outside the body (such as a change in temperature).
The nervous system perceives the change and takes actions to adjust. To perform such sophisticated services,
the nervous system must be highly complex. This lesson provides a general overview of this remarkable system.
The nervous system can be divided into two main parts:
• the central nervous system
• the peripheral nervous system.
THE CENTRAL NERVOUS SYSTEM (CNS)
The CNS is made up of the brain and the spinal chord, and is responsible for processing, interpreting and storing messages, allowing the body to maintain homeostasis and respond to different stimuli. The brain and spinal cord are the two parts of the CNS.
The Brain
The coordinating and synthesising part of the central nervous system (CNS) is the brain. The brain of a
human is divided into several main areas:
• The cerebrum – the largest part of the brain, responsible for the highest kinds of mental activity as well as voluntary muscle control, interpretation of sensations, reasoning, learning and memory. In other words, the thinking part of the brain.
• The cerebellum – governs the co-ordination, adjustment and the smoothing out of movement.
• The olfactory bulb – concerned with the sense of smell, which is the only sense that communicates directly the centre of emotions, the amygdala. This means that the sense of smell is closely associated with our emotions.
• The thalamus – acts as a relay centre for neurons that link the spinal chord to the cerebrum. It has a
twofold function:
- Â It acts as a channel between the sense receptors (all except smell) and the cerebellum.
- Â It plays a role in controlling the cycle of sleep and wakefulness.
• The hypothalamus – includes the important pituitary gland, an endocrine gland whose hormones
influence body growth, reproduction, lactation, and the water balance in the kidneys. It also generally
influences the activity of cells. Its role from a psychologists viewpoint might be summarised as:
- Â Controlling patterns of eating, drinking and sexual behaviour.
- Â Homeostasis – An optimal level of organic function, usually maintained by a regulatory
- mechanism. (i.e. the maintenance of a healthy balance of temperature, heart rate and blood
- pressure).
- Â Hormonal activity
• The medulla oblongata – also known as the brain stem. It connects the brain with the spinal chord, and a number of the cranial nerves leave the brain at this point. It contains a number of reflex centres which
control the heart beat, circulation, respiration, swallowing, and various digestive functions.
Other main parts of the brain
The reticular system – a network of neural pathways throughout the central core which is connected to the
sense receptors. It acts as a filter for all incoming information and thus plays a role in our attention,
awareness and arousal.
The limbic system – a composite of structures which surround the central core. This system acts as a seat for our drives and emotions. It aids the hypothalamus in kerbing instinctive distress, and part of this system is also involved with memory capacity.
The Spinal Cord
The spinal cord is a tissue mass inside the vertebral canal, protected by the bone of the vertebrae. It also
consists of:
• Spinal nerves – 31 pairs of nerves originating from posterior and anterior roots on the spinal cord.
• Spinal meninges – membranes covering the central nervous system in the spine.
Definitions:
Voluntary – Unforced or self-motivated.
Receptor – A sensory nerve ending that
responds to a particular kind of stimulus, found in
the sense organs and on the skin. |
The spinal cord is the continuation of the medulla oblongata, and sends messages between the brain and part of the body. The cord travels down the length of the spinal column protected inside the vertebrae. It is divided into segments.
Each segment gives rise to a pair of spinal nerves which travel from the spinal cord into the body through spaces in the vertebrae. In the centre of the spinal cord there is a canal filled with fluid called the cerebrospinal fluid. This fluid circulates up and down the spinal cord and into cavities of the brain. Impulses are transmitted from the tissues of the body to the brain along the spinal cord.
Reflex Actions
A reflex is an automatic (unlearned) response to a stimulus, caused by the reflex arc, the neural circuit that links the spinal to other parts of the body, permitting the body to quickly respond to stimuli. A reflex action is the response of a motor neuron to a stimulus from a sensory neuron.
There are simple and complex reflex actions. Simple ones occur in the spinal cord where the motor and sensory neurones join at the reflex arc.
With more complex reflexes, the stimulus is passed along to the brain which then sends out its own stimulus or message on what action to take.
The medulla oblongata has reflex centres which control the actions of the heart, expansion and contraction of blood vessels and such actions as swallowing, vomiting, coughing and sneezing. The reflex centres in the cerebellum control movement and posture while those in the hypothalamus regulate temperature and the water balance.
THE PERIPHERAL NERVOUS SYSTEM (PNS)
The PNS consists of nerves in the head (cranial nerves), nerves from the spine (spinal nerves), a selfgoverning nervous system that deals with reflexes (the autonomic nervous system), and a system of glands that produce hormones in response to stimuli (the endocrine system).
The PNS contains all the nerves outside the CNS, and is therefore crucial in receiving sensory and other stimuli and transmitting messages to different parts of the body.
Neurons
A neuron is a nerve cell capable of receiving and transmitting an impulse (message). These cells are joined to each other to form chains of neurons, some quite short and some long, along which nerve impulses travel.
Key Terms
• Nucleus – The nucleus contains the nucleolus; this is the part of the cell which holds the
genetic material, the chromosomes and chromatin which are concerned with reproduction
of the cell.
• Dendrites – branches of the cell that receives and carries impulses towards the cell body.
• Cell body – The mass of cytoplasm containing the nucleus (i.e. close to the nucleus),
distinct from long branches of cell which extend away from the proximity of the nucleus.
• Axon – The long process of a nerve cell that conducts impulses away from the cell body.
• Myelin sheath – A covering made up of layers of lipids and proteins covering Schwann cells and oligodendrocytes around axons of many neurones. Not all neurons have myelin sheaths.
Sensory neurons in the PNS receive messages from special receptors in the skin, muscles etc. and carry
them to the spinal cord, which sends them to the brain. An example of an impulse carried in this sort of
neuron would be the sensation registered by nerve ends in a finger when it is burnt by a flame.
The impulse is first received in the finger and then sent to the central nervous system for decoding. The impulse in a
sensory neuron begins in the nerve ends then travels along the dendron to the cell body. (A dendron is a
filament that carries an impulse to a neuron)….
   This course is accredited by ACCPH and allows you to join as a professional member after completion. Membership allows you to add the letters MACCPH after your name (post  nominals).
