The Nervous System

Structures and Processes

Central Nervous System

Peripheral Nervous System

Structures and Processes

HomeostasisOrganization Cells of the Nervous SystemThe Nerve ImpulseSynaptic Transmission

Homeostasis• Homeostasis is the state of relative stability within is the state of relative stability within

the bodythe body• Homeostasis is achieved through negative feedback Homeostasis is achieved through negative feedback

mechanismsmechanisms• Homeostasis regulates such factors as blood pressure, Homeostasis regulates such factors as blood pressure,

body temperature, , blood glucose concentration and and many other processesmany other processes

• The The nervous system and endocrine system control system and endocrine system control homeostasishomeostasis

Organization of the Nervous System

• The The nervous system is made up of two is made up of two divisions:divisions:

1.1. The central nervous system (The central nervous system (CNS) ) consists of the brain and spinal cordconsists of the brain and spinal cord

2.2. The peripheral nervous system (PNS) The peripheral nervous system (PNS) consists of consists of somatic and autonomic nerves

Cells of the Nervous System

• The nervous system consists of The nervous system consists of neurons and glial cells

• Neurons are the basic functional units of the Neurons are the basic functional units of the nervous systemnervous system

• Glial cells physically support the fragile Glial cells physically support the fragile neuronsneurons

• Neurons are organized into bundles called Neurons are organized into bundles called nerves

Cells of the Nervous System

• There are three types of neuronsThere are three types of neurons1. Sensory neurons carry nerve impulse from carry nerve impulse from

receptors to the central nervous systemreceptors to the central nervous system2. Interneurons carry nerve impulses within the carry nerve impulses within the

central nervous systemcentral nervous system3. Motor neurons carry nerve impulses from the carry nerve impulses from the

central nervous system to the effectors (muscles central nervous system to the effectors (muscles or glands)or glands)

Cells of the Nervous System

• Neurons relay nerve impulses along Neurons relay nerve impulses along neural pathways to create either neural pathways to create either cognitive responses or reflex responses

The Nerve Impulse• A nerve impulse is an A nerve impulse is an electrochemical charge that that

travels along the length of a neurontravels along the length of a neuron• Nerve impulse transmission involves several stepsNerve impulse transmission involves several steps1. Resting membrane potential is established so the is established so the

neuron is polarizedneuron is polarized2.2. The neuron is stimulated above its threshold The neuron is stimulated above its threshold

potentialpotential

The Nerve Impulse3.3. An An action potential is created at one point on the is created at one point on the

membrane so that part of the neuron is membrane so that part of the neuron is depolarizeddepolarized

4.4. The depolarized zone The depolarized zone cascades along the neuron along the neuron towards the axon terminalstowards the axon terminals

5.5. The neuron repolarizes to establish resting The neuron repolarizes to establish resting potential once again potential once again

• A nerve impulse can be represented by a A nerve impulse can be represented by a graph

Synaptic Transmission

• Once the nerve impulse reaches the axon Once the nerve impulse reaches the axon terminal of the presynaptic neuron it must terminal of the presynaptic neuron it must cross the synapse to the dendrite of the the synapse to the dendrite of the postsynpatic neuron postsynpatic neuron

• The gap between neurons is called a The gap between neurons is called a synapse• The gap between a motor neuron and a The gap between a motor neuron and a

muscle fiber is called a neuromuscular muscle fiber is called a neuromuscular junctionjunction

Synaptic Transmission

• The nerve impulse crossing the synapse The nerve impulse crossing the synapse involves involves several steps

1.1. The depolarized zone reaches the axon The depolarized zone reaches the axon terminal of the presynaptic neuron which terminal of the presynaptic neuron which triggers vesicles to migrate towards the triggers vesicles to migrate towards the synapsesynapse

2.2. The vesicles release neurotransmitters into The vesicles release neurotransmitters into the synapsethe synapse

Synaptic Transmission

3.3. The neurotransmitters diffuse across The neurotransmitters diffuse across the synapse to receptors on the the synapse to receptors on the postsynaptic neuronpostsynaptic neuron

4.4. Ion channels on the postsynaptic Ion channels on the postsynaptic neuron open to cause either neuron open to cause either depolarization or hyperpolarization depolarization or hyperpolarization of the membraneof the membrane

Synaptic Transmission

• Excitatory neurotransmitters open sodium open sodium channels and cause depolarization while channels and cause depolarization while inhibitory neurotransmitters open potassium inhibitory neurotransmitters open potassium channels and cause hyperpolarizationchannels and cause hyperpolarization

• Acetylcholine is an excitatory Acetylcholine is an excitatory neurotransmitter that must be broken down neurotransmitter that must be broken down by an enzyme (by an enzyme (cholinesterase) so that the ) so that the postsynaptic neuron can repolarizepostsynaptic neuron can repolarize

Synaptic Transmission

• Summation is the combined effect of all is the combined effect of all neurotransmitters from the pre-neurotransmitters from the pre-synaptic neurons on the post-synapatic synaptic neurons on the post-synapatic neuron neuron

Central Nervous System

The Spinal CordThe Brain

The Spinal Cord• The The spinal cord is a column of nerve tissue that is a column of nerve tissue that

extends out of the skull from the brain and extends out of the skull from the brain and downward through a canal within the back downward through a canal within the back bonebone

• The spinal cord is protected by the The spinal cord is protected by the vertebrae of of the backbonethe backbone

• Spinal nerves contain sensory and motor nerves contain sensory and motor nerves carry impulses into and out of the spinal cord, carry impulses into and out of the spinal cord, respectively respectively

The Spinal Cord• The dorsal root of each spinal nerve The dorsal root of each spinal nerve

contains sensory neuronscontains sensory neurons• The ventral root of each spinal nerve The ventral root of each spinal nerve

contains motor neuronscontains motor neurons• The cells of the spinal cord are either grey The cells of the spinal cord are either grey

matter or white matter and are protected matter or white matter and are protected by the by the cerebrospinal fluid and the and the meninges

The Brain• The The brain is subdivided into three is subdivided into three regions1.1. Forebrain: consists of the thalamus, Forebrain: consists of the thalamus,

hypothalamus, corpus callosum and cerebrumhypothalamus, corpus callosum and cerebrum2.2. Midbrain: consists of neurons that relay Midbrain: consists of neurons that relay

impulses between the forebrain and the impulses between the forebrain and the hindbrainhindbrain

3.3. Hindbrain: consists of the cerebellum, medulla Hindbrain: consists of the cerebellum, medulla oblongata and ponsoblongata and pons

The Brain• The cerebrum is the conscious part of the brainThe cerebrum is the conscious part of the brain• The surface of the cerebrum is called the The surface of the cerebrum is called the

cerebral cortex• The cerebral cortex is divided into hemispheresThe cerebral cortex is divided into hemispheres• The hemispheres are connected through the The hemispheres are connected through the

corpus callosum• Each hemisphere is divided into four Each hemisphere is divided into four lobes

(parietal, temporal, frontal and occipital)(parietal, temporal, frontal and occipital)

Peripheral Nervous System

The Somatic SystemThe Autonomic System

The Somatic System• The somatic nervous system:The somatic nervous system:

1.1. Under voluntary controlUnder voluntary control2.2. Controls the skeletal muscles of the Controls the skeletal muscles of the

head, torso and limbshead, torso and limbs3.3. Includes Includes spinal nerves and most and most

cranial nerves

The Autonomic System• The autonomic nervous system:The autonomic nervous system:

1.1. Under involuntary controlUnder involuntary control2.2. Controls the cardiac and smooth muscles of the Controls the cardiac and smooth muscles of the

circulatory, respiratory, excretory, endocrine and circulatory, respiratory, excretory, endocrine and digestive systemsdigestive systems

3.3. Comprised of two divisionsComprised of two divisionsa)a) Sympathetic: prepares the body for stressSympathetic: prepares the body for stressb)b) Parasympathetic: returns the body to normal Parasympathetic: returns the body to normal

after stressafter stress