The Nervous System

Functions of the Nervous System

• 1. Monitors internal and external environment• 2. Take in and analyzes information• 3. Coordinates voluntary and involuntary

responses.

Organs of the Nervous System

• Brain and Spinal Chord (CNS)• Sensory Receptors of Sense Organs (eyes, ears

etc) • Nerves connect nervous system with other

systems

Divisions of the Nervous System

• 1. Central Nervous System– Spinal Chord and Brain– Processing coordination of stimulus and response

2. Peripheral Nervous System- All neural tissue outside the CNS

- Delivers sensory information to the CNS and carries motor commands to the effectors

Functions of the CNS

• Are to process and coordinate:• - sensory data:

• From inside and outside the body

– Movement: • Control activities of peripheral organs (e.g. skeletal

muscles)

– Higher functions of the brain• Intelligence, memory, learning, emotion

Functions of the PNS

• 1. Deliver sensory information to the CNS• 2. Carry commands to peripheral tissues and

systems

Nerves

• Also called peripheral nerves: – Bundles of axon with connective tissues and blood

vessels– Carry sensory information and motor commands

in PNS: • Cranial nerves: connects to brain (12 pairs)• Spinal nerves: attach to spinal chord (31 pairs)

Divisions of the PNS

• Afferent Division:– Carries information from PNS to CNS

• Efferent Division:– Carries motor commands from CNS to PNS – Has somatic and autonomic components

The Efferent Division of the PNS

• Somatic Nervous System (SNS)– Controls skeletal muscle contraction• Voluntary muscle contractions• Reflexes

• Autonomic Nervous System (ANS)– Controls subconscious actions • Contraction of smooth and cardiac muscle• Glandular secretions

The Autonomic Nervous System Splits

• Parasympathetic Nervous System• Sympathetic Nervous System

Neural Tissue

• Contains 2 kinds of cells– Neurons• Cells that send and receive signals

– Neuroglia• Cells that support and protect nerves

Neurons

• The basic functional units of the nervous system

• Parts of a neuron – Cell body (Soma)– Short, branched dendrites – Long, single axon

Structure of a Neuron

Dendrites

• Highly branched• Dendritic spines:– Receive information from other neurons– 80-90% of neuron surface area

The Axon

• Long• Carries electrical signal (action potential) to

target• Axon structure is critical to function

Nodes and Internodes

• Internodes– Myelinated segments of axon

• Nodes– Also called nodes of Ranvier– Gaps between internodes– Where axons may branch

The Synapse• Area where a neuron communicates with another cell

Synapse

• Areas where a neuron communicates with another cell

• Presynaptic Cell– Neuron that sends message

• Postsynaptic Cell – Cell that receives message

• Synaptic Cleft– Gap that separates the presynaptic membrane

and the postsynaptic membrane

The Synaptic Knob

• Is expanded area of axon• Contains synaptic vesicles of

neurotransmitters– Chemical messengers– Released at presynaptic membrane– Affect receptors of postsynaptic membrane

Functional Classifications of Neurons

• Sensory Neurons– Deliver information to CNS

• Motor Neurons– Stimulate or inhibit peripheral tissues

• Interneurons– Located between sensory and motor neurons – Analyze inputs, coordinates outputs

Neuroglia

• Half the volume of the nervous system

• Many types of neuroglia in the CNS and PNS

Neuroglia Functions

• Line of central canal of spinal chord and ventricles of brain

• Repair damaged neural tissue• Processes contact between other neuron cell

bodies

Neuorglia

• Wrap around axons to form myelin sheaths (Schwann Cells)– Increases speed of action potentials– Myelin insulates myelinated axons– Makes nerves appear white (white matter)

White and Grey Matter

• White Matter– Regions of CNS with many myelinated nerves

• Grey Matter– Unmyelinated areas of CNS