Nervous System

Myelin Sheath

"A fatty tissue that protects the axon" External covering of axon. A fatty layer of tissue to protect the axon. Aids in the speed of transmission of neural impulses. Multiple sclerosis occurs when the immune system attacks its own myelin sheath.

Axon

"A thin fibre that carries the neural message away from the soma" The long stem (thin fibre) of a neuron. Carries information away from the cell body and throughout the brain and nervous system. Important for speed of transmission of neural impulses. External covering known as the myelin sheath. Some are only 0.1 millimetres long whilst others can stretch to over a metre.

Interneurons

"Interneurons carry information directly between sensory and motor neurons. They are involved in the reflex arc" Located in the CNS. Majority of human responses require both sensory and motor information to be integrated. Specialised nerves that form a direct connection between motor neurons and sensory neurons. Most numerous type of neuron in the CNS due to its demanding role. Role: reflex arc / spinal reflex Interneurons are activated when sensory neurons receive an intense sensation. Interneurons in the spinal cord relay the information from sensory neurons directly to motor neurons and the involvement of the brain in interpreting the sensory information is bypassed. As a result, the response is instant and enhances survival.

Axon Terminal

"The branches at the end of the axon" Axon terminals are where chemical substances are released to enable communication between neurons. When the chemical is released it is received by the dendrites of another neuron. A chemical connection, known as the synapse (or synaptic gap) bridges the gap between two neurons. Neurotransmitters carry chemical messages across the synapse to the dendrite o a receiver neuron. Thus, neural energy is transmitted from one neuron to another, enabling it to travel from the sensory receptor site to the brain.

Soma (cell body)

"The cell body that sends neural messages down the axon" The body of the neuron. Where the dendrites are attached to. Responsible for keeping the cell alive and functioning. Messages from dendrites cause the soma to send a nerve impulse to the axon.

Motor Neurons (efferent)

"The neurons carry commands from the brain to the body's muscles, organs and glands to enable movement" Located in the PNS. When sensory information reaches the brain, it is then interpreted and information is made about what an appropriate response should be. The response usually involves a degree of movement. Motor neurons carry this information from the CNS to the PNS for te reponse to be initiated. Also called efferent neurons as the information motor neurons carry is travelling away from the brain. The motor information causes the muscles to relax or contract, and glands to increase or decrease secretions. Also affects activity level of internal organs to that a specific type of movement can be enacted. Voluntary movement is also initiated via information passed by motor neurons.

Sensory Neurons (afferent)

"The neurons detect energy from the environment and carry information about it to the CNS" Located in the PNS. When the PNS relays sensory information to the CNS, this is carried out by sensory neurons. Specialised neurons that detect specific forms of external energy (such as light) and itnernal stimulation from the body's muscles, organs and glands. Also called afferent neurons due to the direction the information travels.

Dendrites

"Where incoming information is first received" Dendrites branch out from the main body of the neuron. Each nueron body can have many dendrites that extend out to receive the incoming message but only one message can be received at any one time. Receptor sites are found on dendrites.

Corpus Callosum

A band of nerve fibres that enable communication between the two hemispheres. Buried deep beneath the brain.

Peripheral Nervous System

A support network of information carrying nerves to connect the various body parts to it. Consists of all the neurons outside the CNS including muscles, organs and glands. Two main functions - relay sensory information to the CNS, and to receive motor information from the CNS. Done via nerve cells called neurons which are the basic building blocks of the nervous system. Divided into two sub-systems.

Fight-Flight Response

An automatic response activated by the sympathetic nervous system that prepares the body to deal with a potential threat or danger. It is the body's automatic decision to confront the threat (fight) or flee (run). Both of these actions require a state of arousal to maximise our chances of survival.

Action Potential

At action potential (neural impulse) messages sweep down the axon at 333 kmph. During action potential, the axon membrane is pierced by tiny molecular tunnels called ion channels. These channels are usually blocked by molecules that act like gates or doors but during action potential, the gates open to allow positively charged sodium ions to rush into the axon. The channel first opens near the soma then gate after gate opens down the axon as the action potential runs along.

Sympathetic Nervous System

Branch of the ANS that dominates when we are highly aroused or needing sudden burst of energy. The sympathetic nervous system increases arousal of the muscles, organs and glands and prepares the body for vigorous activity. Arouses us for defensive action. Pupils dilate, heart accelerates, bladder constricts, lungs increase, adrenal glands release adrenalin, stomach decreases contractions.

Neurotransmitters

Communications between neurons are chemical. The rush of action potential causes synaptic vesicles found in the axon terminal to open and these synaptic vesicles contain chemical substances called neurotransmitters. Neurotransmitters are chemicals that alter activity in neurons. Eg. serotonin (memory and emotions) and dopamine (voluntary movement) Neurotransmitters are released into the synaptic gap and cross over the gap and attach to special receptor sites on the receiving neuron.

Central Nervous System

Comprised of the brain and spinal cord.

Midbrain

Connected to the forebrain and hindbrain by many nerve fibre systems. Controls motor reactions and is involved in many of our reflex responses.

Spinal Cord

Delicate cable of nerve fibres that stretches from the base of the brain to the lower back. Connects the brain to the rest of the body. Receives sensory information brought in by the peripheral nervous system and conveys it to the brain for processing and interpretation.

Autonomic Nervous System

Division of the PNS that control involuntary functions of our internal muscles, organs and glands such as hear rate and breathing rate. The autonomic system can be further subdivided into two other systems - the sympathetic nervous system, and the parasympathetic nervous system. These two systems are always active, although one dominates in functioning and their combined activity determines if our body is relaxed or in a heightened state of arousal.

Biofeedback

Exerting control over muscles and organs that usually function independently. Receiving information or "feedback" regarding our heart rate and other physiological responses so that we can attempt to exert control over speeding them up or slowing them.

Somatic Nervous System

Governs our voluntary actions through its control of our skeletal muscles. Receives motor messages from the CNS and transports these messages to muscles in specific body regions. Has a sensory function where the sensory neurons relay messages to the brain providing information of pain, vision, touch and taste.

Left Hemisphere

Hemispheric specialisation of the left hemisphere is its control of language abilities, logic and mathematical abilities and voluntary movement of the right hand side of the body.

Right Hemisphere

Hemispheric specialisation of the right hemisphere is its control and dominance in spatial abilities; creativity, such as music and art appreciation; and voluntary control of the left hand side of the body.

Cerebral Cortex

Largest part of the forebrain. Thin, but contains 70% of neurons in the CNS Involved in higher order functions - planning, reasoning, language abilities, voluntary movement, spatial awareness, creativity. Divided into the left and right hemisphere which are structurally separated and communicate via the corpus callosum.

Forebrain

Located towards the top and front of the brain. Largest and most complex region of the brain. Acts as the brain's managing director - has control of many cognitive functions. Region where we do out thinking and planning, also involved in initiating responses to incoming stimuli.

Resting Potential

Neurons are at its resting potential when the neuron is at rest and is not working. Neurons are rarely at rest and messages arrive from other neurons constantly.

Communication Between Neurons

Neurons communicate using electrochemical energy. While waiting for a message, a neuron has a resting potential. When a neurotransmitter is received, this fires an action potential. The action potential races down the axon to the axon terminal, causing synaptic vesicles to open. These synaptic vesicles contain neurotransmitters which are released across the synaptic gap and received by the receptor site of the next neuron's dendrite. This, in turn, fires the action potential in the next neuron and the process repeats until the message reaches its destination.

Hindbrain

Often referred to as the brain stem. Located at the base of the brain near the back of the skull. Responsible for the control of our basic survival functions such as heart rate, breathing, sleep, arousal and reflex actions. Lower brain functions all occur without any conscious effort.

Parasympathetic Nervous System

The system responsible for calming down the body and reversing the effects of the SNS and returning the body's internal systems to homeostasis after the threat has passed. Pupils constrict, heart decreases, bladder relaxes, lungs decrease, adrenal glands inhibit adrenalin release, stomach increases contractions.

Nervous System

This system acts as the body's control system and is necessary to protect the body from changes in the internal and external environment. The human nervous system is divided into two major parts - the central nervous system and the peripheral nervous system.

Parts of a Neuron

Though with a similar structure, neurons are all different in size and shape. - Dendrites - Soma (cell body) - Nucleus - Axon - Myelin Sheath -Axon Termial - Synapse

Neurons

Types of neurons: sensory neurons, motor neurons, interneurons

Brain

Weighs a little over 1.5 kg and consists of over 100 billion neurons. Can be structurally broken down into three main areas - forebrain, midbrain and hindbrain.