The Nervous System

• A network of billions of nerve cells linked together in a highly organized fashion to form the rapid control center of the body.

• Functions include:– Integrating center for homeostasis,

movement, and almost all other body functions.

– The mysterious source of those traits that we think of as setting humans apart from animals

Performance of normal voluntary movement, Performance of normal voluntary movement, the integrity of two sets of neurons is importantthe integrity of two sets of neurons is important

Upper motor neuronesUpper motor neuronesNeurons originating in the cerebral cortex and the Neurons originating in the cerebral cortex and the brain stembrain stemSynapse directly or indirectly with the anterior horn Synapse directly or indirectly with the anterior horn cells or with the motor neurones of the cranial nervescells or with the motor neurones of the cranial nervesGrouped into pyramidal and extrapyramidal systemsGrouped into pyramidal and extrapyramidal systems

Lower motor neuronesLower motor neuronesMotor cranial nuclei and their axons, i.e. motor fibres Motor cranial nuclei and their axons, i.e. motor fibres of the cranial nerves (3of the cranial nerves (3rdrd, 4, 4thth, 5, 5thth, 6, 6thth, 7, 7thth, 9, 9thth, 10, 10thth, 11, 11thth and 12and 12thth))In the spinal cord they include the anterior horn In the spinal cord they include the anterior horn motor neurones and their axons, i.e. the motor motor neurones and their axons, i.e. the motor nerves to skeletal musclesnerves to skeletal muscles

Basic Functions of the Nervous System

1. Sensation• Monitors changes/events occurring in and

outside the body. Such changes are known as stimuli and the cells that monitor them are receptors.

2. Integration• The parallel processing and interpretation of

sensory information to determine the appropriate response

3. Reaction• Motor output.

– The activation of muscles or glands (typically via the release of neurotransmitters (NTs))

Nervous vs. Endocrine System

• Similarities:– They both monitor stimuli and react so as to

maintain homeostasis.

• Differences:– The NS is a rapid, fast-acting system whose

effects do not always persevere. – The ES acts slower (via blood-borne chemical

signals called H _ _ _ _ _ _ _) and its actions are usually much longer lasting.

Organization of the Nervous System

• 2 big initial divisions:1. Central Nervous System

• The brain + the spinal cord– The center of integration and

control2. Peripheral Nervous System

• The nervous system outside of the brain and spinal cord

• Consists of:– 31 Spinal nerves

» Carry info to and from the spinal cord

– 12 Cranial nerves » Carry info to and from the

brain

Brain Regions

1. Cerebrum

2. Diencephalon

3. Brainstem

4. Cerebellum

Cerebellum

Cerebral Cortex

• 3 types of functional areas:1. Motor Control voluntary

motor functions

2. Sensory Allow for conscious recognition of

stimuli

3. Association Integration

Cortical Motor Areas

1. Primary Motor Cortex

2. Premotor Cortex

3. Broca’s Area

4. Frontal Eye Field

1.Primary motor cortex

3.Broca’s Area

2.Premotor cortex

4.Frontal Eye Field

Primary (Somatic) Motor Cortex

• Located in the precentral gyrus of each cerebral hemisphere.

• Contains large neurons (pyramidal cells) which project to SC neurons which eventually synapse on skeletal muscles – Allowing for voluntary motor

control.– These pathways are known

as the corticospinal tracts or pyramidal tracts.

Primary (Somatic) Motor

Cortex• Somatotopy

– The entire body is represented spatially in the primary motor cortex,

_ i.e., in one region we have neurons controlling hand movements and in another region leg movements, etc.

• What does it mean to say that motor innervation is contralateral?

Sensory Areas• Found in the parietal, occipital, and

temporal lobes.

1. Primary somatosensory cortex2. Somatosensory association cortex3. Visual areas4. Auditory areas5. Olfactory cortex6. Gustatory cortex7. Vestibular cortex

Primary Somatosensory Cortex• Found in the

postcentral gyrus.• Neurons in this

cortical area receive info from sensory neurons in the skin

• and from proprioceptors which monitor joint position.

• Contralateral input.

Somatosensory Association Cortex

• Found posterior to the primary somatosensory cortex and is neurally tied to it.

• Synthesizes multiple sensory inputs to create a complete comprehension of the object being felt.– How would damage to

this area differ from damage to the primary somatosensory cortex ?

Basal Nuclei• Info arrives at the caudate nucleus and the putamen from sensory, motor,

and association areas of the cortex.• Processing and integration occurs w/i the nuclei and then info is sent

from the globus pallidus to the motor cortex via the thalamus.• The basal nuclei alter motor commands issued by the cerebral cortex via

this feedback loop.

Parkinson’s Disease• Each side of the midbrain contains a nucleus called

the substantia nigra.• Neurons in the substantia nigra inhibit the activity of

basal nuclei by releasing dopamine.

Damage to SN neurons

Decrease in dopamine secretion

Increased activity of basal nuclei

Gradual increase in muscle tone

Appearance of symptoms of Parkinson’s disease: tremor, slow movement, inability to move, rigid

gait, reduced facial expression

Diencephalon

• Forms the central core of the forebrain

• 3 paired structures:

1. Thalamus

2. Hypothalamus

3. Epithalamus

All 3 are gray matter