The nervous system

Role of the nervous system The nervous system controls all of the body’s activities. It receives information from the outside world, takes it to your brain, processes it, and decides how you will respond.

The nervous system is divided into two parts: The basics The nervous system is divided into two parts: The Central Nervous System (CNS) which is composed of the the brain and spinal cord The Peripheral Nervous System (PNS) which is composed of nerves.

Stimulus A stimulus is anything that can be perceived, which can trigger a reaction. Examples:

Sensory Receptors These are specialized nerves that pick up stimuli and transform them into electrical impulses. Examples:

Sensory nerve This is the message’s pathway to the central nervous system (brain and spinal cord).

Motor nerve This is the nerve impulse’s pathway from the central nervous system to a muscle to produce a movement (whether voluntary or involuntary).

Nerve impulses can reach 430 km/hr Messages travel fast! Nerve impulses can reach 430 km/hr

How does this work? Messages travel through your nervous system in the form of electrical impulses. They travel through nervous tissue, which is composed of cells called neurons.

Neuron anatomy Dendrites Axon terminal Nucleus Cell body Myelin sheath Axon

Synapse Neurons are aligned such that the axon terminal of one is immediately adjacent to the dendrite of another. The small gap between them is called the synapse.

Synapse When one neuron is stimulated, it sends its electric impulse down its axon, causing it to release chemicals into the synapse that will bond with the next neuron. These chemicals care called neurotransmitters.

Some neurotransmitters you may have heard of… Dopamine: The “reward” neurotransmitter associated with feelings of extreme pleasure Serotonin: Influences our mood, appetite, memory, etc. Epinephrine: Increases blood flow to muscles, responsible for “fight or flight” response.

How are your neurons different than other cells in your body? They can live as long as you do (i.e. around 100 years!). Your RBCs only live about 4 months. They consume a lot of glucose and oxygen. In fact, 25% of your body’s caloric energy is used by your brain alone. There are 86 billion neurons in your body, and they are never replaced… so take good care of them.

Structure of the brain The brain is protected by the skull, the spinal cord is protected by the spine. Both the brain and spinal cord are also protected by a thin membrane called the meninges.

The brain is divided into 3 regions

Cerebrum Command centre for: All voluntary movements Interpretation of all senses Intelligence Emotions

Cerebrum Composed of grey matter (mostly cell bodies) and white matter (mostly axons)

Cerebrum We also divide the cerebrum into different regions to help localize certain functions. These regions are called lobes.

This controls balance and movement. It also helps us multitask. Cerebellum This controls balance and movement. It also helps us multitask.

Brainstem (or medulla) This controls internal stimuli and involuntary movements.