Neurons and the Nervous System

Nervous System

– Central nervous system (CNS):• Brain• Spinal cord

– Peripheral nervous system (PNS):• Sensory neurons• Motor neurons (somatic and

autonomic)

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Central Nervous System (CNS)Central Nervous System (CNS)

BrainBrain Spinal CordSpinal Cord

Peripheral Nervous System (PNS)Peripheral Nervous System (PNS)

Sensory NeuronsSensory NeuronsMotor NeuronsMotor Neurons

Somatic Nervous System• voluntary movements via

skeletal muscles

Somatic Nervous System• voluntary movements via

skeletal muscles

Autonomic Nervous System• organs, smooth muscles

Autonomic Nervous System• organs, smooth muscles

Sympathetic- “Fight-or-Flight” responses

Sympathetic- “Fight-or-Flight” responses

Parasympathetic - maintenance

Parasympathetic - maintenance

The Nervous SystemThe Nervous SystemThe Nervous System

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Divisions of the autonomic nervous system

The Nervous System

• A physical organ system like any other

• The main cell of the nervous system are:

– Neurons

The Neuron• The basic functional

unit of the nervous system.

• Function: Send impulses to and from the CNS and PNS

Neuron Structure

• Dendrite Fine hair-like extensions on the end of a neuron.–Function: receive incoming stimuli.

• Cell Body or Soma The control center of the neuron. –Function: Directs impulses from the

dendrites to the axon.• Nucleus Control center of the

Soma. –Function: Tells the soma what to do.

• Axon Pathway for the nerve impulse (electrical message) from the soma to the opposite end of the neuron.

• Myelin Sheath An insulating layer around an axon. Made up of Schwann cells.

• Nodes of Ranvier Gaps between schwann cells. – Conduction of the impulse. (Situation

where speed of an impulse is greatly increased by the message ‘jumping’ the gaps in an axon).

Types of Neurons• There are 3 types of neurons.

1. Sensory Neurons Neurons located near receptor organs (skin, eyes, ears). Function: receive incoming stimuli from the

environment.

2. Motor Neurons Neurons located near effectors (muscles and glands) Function: Carry impules to effectors to initiate a

response.

3. Interneurons Neurons that relay messages between other neurons such as sensory and motor neurons. (found most often in Brain and Spinal chord).

Types of Neurons

Sensory vs. Motor Sensory vs. Motor

e.g., skin

e.g., muscle

Gray’s Anatomy 38 1999

sensory nerve

motor nerve

Neurons that send signals from the senses, skin, muscles, and internal organs to the CNS

Neurons that transmit commands from the CNS to the muscles, glands, and organs

Nerves

• Nerves Collections of neurons that are joined together by connective tissue.

• Responsible for transferring impulses from receptors to CNS and back to effectors.

Neuron Anatomy and Neural Communication

Neurons

Axon of anotherneuron

Axon of anotherneuron

Cell BodyCell BodyDendritesDendrites

AxonAxon

MyelinSheathMyelinSheath

Dendrites of another neuron

Dendrites of another neuron

Neural Anatomy and communication

Synapse junction between the axon tip of

the sending neuron and the dendrite or cell body of the receiving neuron

tiny gap at this junction is called the synaptic gap or cleft

Specific Parts: The NeuronStructure

Specific Parts: The Neuron Function

Neurons = 3 functions: Reception, Conduction, Transmission

1.3.

2.

Communication

• Impulse releases neurotransmitter from vesicles

• Neurotransmitter enters synaptic gap

• Neurotransmitter binds to receptors on the receiving neuron

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Place of the PNS in the structural organization of the nervous system

CNS

Sensory division Motor division

Autonomic nervous system

Sympathetic division

Parasympathetic division

PNS

Somatic nervous system

Central Nervous SystemThe Brain

• cerebral cortex: the covering, where most mental processes take place

• The brain is divided into two halves (cerebral hemispheres) separated by a deep fissure– hemispheres control

opposite side of body (e.g. right-handers’ writing is controlled by the left hemisphere)

Our Divided Brain• cerebral

hemispheres connected by the:– corpus callosum,

a large band of neural fibers that transmits messages between hemispheres

Structure of the Cortex• cerebral cortex divided

into lobes, or regions of the brain

– Each lobe is (roughly) responsible for different higher-level functions, but remember that they do not work merely in isolation.

Structure of the Cortex

• occipital lobe: brain lobe at the back of the head

– responsible primarily for vision

Structure of the Cortex• temporal lobe: the brain

lobe under the temples, in front of the ears

– many functions, including receiving and processing sounds, comprehending language committing information to long term memory, emotion

Structure of the Cortex• parietal lobe: brain

lobe at the top and center/rear of the head

–involved in registering spatial location, body awareness, touch and pressure, taste

Structure of the Cortex• frontal lobe: the brain lobe

located behind the forehead

– Movement of body, personality, concentration, planning, problem solving, meaning of words, emotional reactions, speech and smell.

– In many ways, the frontal lobe is what makes us uniquely human.

Our Divided Brain• cerebral

hemispheres connected by the:– corpus callosum,

a large band of neural fibers that transmits messages between hemispheres