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The Human Nervous System

Complex system of nerve cells that carry messages to and from the brain and spinal cord to different parts of the body and so helps all the parts of the body communicate with each other. Divided into two systems: central nervous system (CNS) and the peripheral nervous system (PNS).

Nerve cells


CNS


PNS

CNS

Brain and Spinal cord

PNS

The Somatic Nervous System and The Autonomic Nervous System

SNS and ANS

The Autonomic Nervous System

The Sympathetic Branch and The Parasympathetic Branch. Responsible for carrying only motor information from and to the CNS. Controls internal organs and glands in the body such as breathing, heart rate and digestion. Self-regulating as vital-bodily functions would not work so well if we had to think about them.

SB and PSB

The Brain

Centre of all conscious awareness. Cerebral cortex, is highly developed in humans

Conscious awareness


Cerebral cortex

The Spinal Cord

Extension of the brain. Responsible for relaying information between the brain and the rest of the body. Also contains circuits of nerve cells that enable us to perform reflex actions such as pulling your hand away from a hot plate.

Extension of the brain

The Somatic Nervous System

Carrying sensory and motor information to and from the CNS. SNS controls skeletal, muscle movement and receives information from sensory receptors.

Skeletal, muscle movements

The Sympathetic Nervous System

Responses that help us deal with emergencies. Neurons travel to virtually every organ and gland within the body, preparing the body for rapid action. E.g. the sympathetic nervous system causes the body to release stored energy, pupils to dilate and hair to stand on end. It slows down (inhibits) less important bodily processes, such as digestion and urination.

Deal with emergencies


Fight or Flight System


Release stored energy


Pupils dilate


Inhibits less important

The Parasympathetic Nervous System

Return body to a rest state once emergency has passed. Bodily functions inhibited are returned to normal.

Rest state


Returned to normal

Neurons

Cells that carry information throughout the body. They do this via electrical and chemical signals (neurotransmitters). There are 100 billion neurons in humans and there are three types: sensory, relay and motor.

Carry Information


Neurotransmitters


100 billion


Three types

Structure of a Neuron

Consist of a c ell body, dendrites and an axon. Dendrites at one end of the neuron receive signals from other neurons or from sensory receptors. Dendrites are connected to the cell body, the control centre of the neuron. From the cell body, an impulse is carried along the axon, where it terminates at the axon terminal. The axon is covered in a fatty layer called the myelin sheath that protects the axon and speeds up the electrical transmission of the impulse. If the myelin sheath is damaged, the impulse slows down.

Cell body


Axon


Dendrites


Impulse


Axon terminal


Myelin sheath


Electrical transmission

Sensory Neurons

Carry messages from the sensory receptors in the PNS to the CNS. However, not all information travels as far as the brain, with some neurons terminating in the spinal cord. This allows reflex actions to occur quickly without delay of sending impulses to the brain.

Carry messages


PNS to CNS


Not all to brain


Reflex actions



Relay Neurons

Carry messages from one part of the CNS to another, Most common type of neuron and allow sensory and motor neurons to communicate with each other. Relay neurons usually have shorter dendrites and axons than sensory and motor neurons.

Carry messages


One part of CNS to another


Sensory and motor


Shorter dendrites and axons

Motor Neurons

Carry messages from the CNS to directly or indirectly control muscles. When stimulated, these neurons release neurotransmitters (chemical messengers) that bind to receptors on the muscle and triggers a response which leads to muscle movement. Muscle relaxation is caused by inhibition of the motor neuron.

Carry messages


CNS


Directly or indirectly control muscles


Stimulated


Release neurotransmitters


Bind to receptors

Synaptic Transmission

Process of transmitting messages from one neurons to another neuron. Each neuron is separated by a tiny gap called the synapse. Signals within neurons are transmitted electrically, however signals between neurons are transmitted chemically across the synapse. When the electrical impulse reaches the end of the neuron (the presynaptic terminal at the end of the axon), it triggers the release of neurotransmitters from tiny sacs called synaptic vesicles. These neurotransmitters then diffuse across the synapse and bind to receptor sites on the dendrites of the postsynaptic neuron. The effects of this last until the neurotransmitters travel back where they came from to be taken up again by the presynaptic neuron. Process is known as reuptake which allows the neurotransmitters to be stored again and made available for later use (a sort of recycling program).

One neuron to another


Synapse


Chemically


Presynaptic terminal


Synaptic vesicles


Bind to receptor sites


Postsynaptic neuron


Reuptake


Presynaptic neuron

Neurotransmitters

Chemical messengers that diffuse across the synapse to the next neuron in the chain. Binds to receptor sites on the post-synaptic neuron. Chemical message is converted back into an electrical impulse and the process of transmission begins again in the next neuron. Several dozen types of neurotransmitters, each of which have specialist functions.

Chemical messengers


Diffuse


Synapse


Receptor sites


Post-synaptic neuron


Electrical impulse

Excitation and Inhibition

- Inhibitory neurotransmitters: (such as GABA) cause inhibition of the post-synaptic neuron, resulting in the neuron becoming negatively charged, decreasing the chance of it firing. Nervous system's 'off switches'. Generally responsible for calming the mind and body.




- Excitatory neurotransmitters: (such as adrenaline which is both a hormone and neurotransmitter) causes excitation of the post-synaptic neuron, resulting the in the neuron becoming positively charged. Nervous system's 'on switches' as they increase chance the neuron will fire and pass on the electrical impulse.

GABA


Postsynaptic neuron


Negatively charged


Off switches


Calms mind and body


Adrenaline


Positively charged


On switches

The Function of the Endocrine System

Chemical system of communication that instructs glands to release hormones directly into the bloodstream. These hormones are carried towards target organs in the body and help regulate many bodily functions. The endocrine and nervous system work closely together to regulate various physiological processes in the human body. E.g. endocrine system involved in stress response, sleeping and waking and the menstrual cycle.

Chemical system of communication


Glands to release hormones


Bloodstream


Regulate many bodily functions


Endocrine and nervous system

Glands

Organs in the body that produce and secrete hormones (chemicals that circulate in the bloodstream) in order to regulate many bodily functions. Major glands include the pituitary gland, adrenal glands and the reproductive organs (testes and ovaries). The 'master' gland is the pituitary gland that controls the release of hormones and all the other glands in the body.

Produce and secrete hormones


Regulate bodily functions


Pituitary gland


Adrenal glands


Reproductive organs


Master gland

Function of Important glands in the body

Pituitary: 'Master gland' - to influence release of hormones from other glands. Regulates many of the body's functions. Controlled by the hypothalamus.




Pineal: Regulates biological rhythms such as the sleep-wake cycle as it facilitates the release of the hormones, melatonin.




Adrenal: An important part of the 'fight or flight' stress response as it releases adrenaline.




Testes: Controls the release of the male sex hormone, testosterone.




Ovaries: Regulates release of oestrogen and progesterone involved in the menstrual cycle.

Pituitary gland


Master gland


Regulates many bodily functions


Hypothalamus


Pineal


Biological rhythms


Sleep-wake cycle


Melatonin


Adrenal


'Fight or flight' stress response


Adrenaline


Testes


Testosterone


Ovaries


Oestrogen


Progesterone


Menstrual Cycle

Flight of Flight Response

Aliens: Acute stressor, triggers


Have: Hypothalamus, directs


Somehow: Sympathetic branch of the ANS sends neurotransmitters


Always: Adrenal medulla, releases


Adored: Adrenaline, activates


Fone: 'Fight or flight', causes


Parties: Physiological reactions

Aliens, triggers


Have, directs


Somehow, sends neurotransmitters


Always, releases


Adored, activates


Fone, causes


Parties

Functional Magnetic Resonance Imaging (fMRI)

Detects changes in blood oxygenation and flow that occur as result of neural activity. Produces 3 dimensional imaging.

Electroencephalogram (EEGs)

Measure electrical activity within brain via electrodes on skull cap. Scan recordings represent brainwave patterns.

Event-related Potentials (ERPs)

Types of brainwaves that relate to a specific function. Uses a statistical averaging technique.

Post-mortem Examinations

Analysis of person's brain following their death. Establishes likely cause of affection and may involve comparison with neurotypical brain.