The Central Nervous System

Brain

Centralnervoussystem(CNS)

Spinalcord

Peripheralnervoussystem(PNS)

Afferentdivision

Efferentdivision

Sensorystimuli

Visceralstimuli

Somaticnervous system

Autonomicnervous system

Motor neurons

Sympatheticnervous system

Parasympatheticnervous system

Skeletal muscle

Smooth muscleCardiac muscleGlands

Effector organs(made up of muscle and gland tissue)

(Input to CNSfrom periphery)

(Output from CNSto periphery)

The nervous and endocrine systems can be compared.

• The nervous system transmits electrical impulses to skeletal muscles and the exocrine glands.

• It is “wired”, sending electrical signals through distinct, highly organized pathways. These pathways have interconnected parts.

• The endocrine system secretes hormones (chemical messengers) into the circulating blood to distant sites in the body.

• These glands are not connected. They are scattered throughout the body.

Other Comparisons between the two systems are:

• Each neuron has a close anatomic relationship to its target cells. It has a narrow range of influence.

• A neuron releases a specific neurotransmitter to a specific target cell.

• The target cells have specific receptors that bind to the neurotransmitter secreted by a neuron.

• Although that neuron can potentially signal other cells, it is limited to the target cells in close proximity to that neuron.

• A group of endocrine cells secretes a specific hormone into the blood. Although the hormone is circulated throughout the body, only specific target cells have receptors for a specific hormone.

• A hormone cannot influence all body cells. It influences the target cells with receptor cells that bind to that hormone.

• The nervous system coordinates rapid, precise responses.

• Its signal is an action potential. The duration of this signal is brief.

• The target cells are skeletal muscles and glands.• The endocrine system controls activities of

longer duration. • This system requires a flow of blood to send a

message. • The effect of a hormone lasts longer.

• The nervous and endocrine systems are interconnected functionally.

• Often they influence the same body process, such as the rate of heartbeat.

• Neuroendocrinology is the study of the relationships between these two systems.

The nervous system has two branches: central (CNS) and

peripheral (PNS).

• The CNS consists of the brain and spinal cord.• The PNS has two main divisions:

– The afferent division sends information to the CNS.– The efferent division sends information away from the CNS

and to effector organs.

• The efferent nervous system consists of two systems. The somatic nervous signals skeletal muscles. The autonomic nervous system signals

• smooth and cardiac muscle plus gland.• The autonomic nervous system has two branches:

sympathetic and parasympathetic.

There are three classes of neurons.

• An afferent neuron sends signals toward the CNS. It generates action potentials from sensory receptors at its peripheral end. It has a long axon and is found mainly in the PNS.

• An efferent neuron sends signals away from the CNS to an effector organ. It has a long peripheral axon in the PNS.

• An interneuron is found entirely within the CNS. It lies between afferent and efferent neurons.

Centralnervous system(spinal cord)

Peripheralnervous system

Axonterminals

Cellbody

Afferent neuron

Centralaxon

Peripheral axon(afferent fiber) Receptor

Interneuron

Efferent neuronEffector organ(muscle or gland)

Axon(efferent fiber)

Axonterminals

* Efferent autonomic nerve pathways consist of a two-neuron chain between the CNS and the effector organ.

Cellbody

Glial cells do not send signals. They support interneurons physically, metabolically, and functionally. There are four main kinds.

• The astrocyte has many functions:– holding neurons together– guiding neurons during development– establishing a blood-brain barrier– repairing brain injuries– playing a role in neurotransmitter activity– taking up excess K+ from the brain ECF

The oligodendrocyte forms myelin sheaths around axons in the CNS.

• Microglia are the immune defense of the CNS.• They are scavengers.• Ependymal cells line the internal cavities of the CNS.

The CNS is protected several ways.

• The cranium encloses the brain. The vertebral column encloses the spinal cord.

• It is wrapped by several meninges: the outer dura mater, the middle arachnoid mate, and the innermost pia mater.

• The brain is surrounded by the cerebrospinal fluid (CSF).

• The blood-brain barrier limits access• of blood-borne substances to the brain.

The CSF is formed and circulates.

• It is produced by the choroid plexuses inside the ventricles.

• It circulates through the ventricles.

• From the fourth ventricle it enters the subarachnoid space, between the arachnoid mater and pia mater.

• Arachnoid villi is this space drain the CSF into the blood.

The blood brain barrier is highly selective.

• It is a series of capillaries that regulate the exchange between the blood and the brain.

• These capillaries allow a limited number of substances to pass from the blood to brain cells.

• The brain needs a constant input of oxygen and glucose from the blood.

The CNS consists of the brain and spinal cord.

• The outline for brain anatomy is:– Brain stem– Cerebellum– Forebrain– Diencephalon– Hypothalamus– Thalamus– Cerebrum– Basal nucleii– Cerebral cortex

Hypothalamus

Brain stem

Cerebral cortex

Thalamus(medial)

Basal nuclei(lateral to thalamus)

Cerebellum

Spinal cord

Midbrain

Pons

Medulla

Brain component

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem(midbrain, pons,and medulla)

The brain stem is continuous with the spinal cord.

• It consists of the midbrain, pons, and medulla. It controls life-sustaining processes such as breathing and digestion.

• The cerebellum is attached to the top rear part of the brainstem.

• It maintains balance, enhances muscle tone, and coordinates/plans skilled voluntary muscle activity.

The diencephalon is on top of the brain stem. It houses the:

• hypothalamus - It controls many homeostatic functions that maintain the stability of the internal environment.

• thalamus - It performs some primitive sensory processing.

The cerebrum is on top of the lower brain regions. It is highly developed in humans.

• The cerebral cortex is its highly convoluted, outer layer of gray matter. It covers an inner core of white matter.

• The cerebrum has an inner core of basal nucleii located deep within the white matter.

The electroencephalogram is a record of postsynaptic activity of cortical neurons.

• It consists of various wave patterns.– It is used as a clinical tool in diagnosis of cerebral dysfunction.

– It can distinguish various sleep stages.

– It is used for legal determination of brain death.

The basal nucleii have an inhibitory role in motor control. Their functions include:

• inhibiting muscle tone throughout the body• selecting and maintaining purposeful muscle activity while

inhibiting useless movement• monitoring and controlling slow, sustained contractions

The thalamus is a relay station. It is also a synaptic integrating center for processing sensory input on its way to the cerebral cortex.

• The hypothalamus regulates many homeostatic functions.

• They include:– controlling body temperature– controlling thirst and urine production– controlling food intake– controlling anterior pituitary hormone secretion– production of posterior pituitary hormones– controls uterine contractions and milk ejection– serves as an ANS coordinating center– plays a role in emotional and behavioral patterns

The limbic system functions with the higher cortex.

• It plays a key role in emotion.• It works with the higher cerebral cortex

to control behavioral patterns.• The limbic system has reward and

punishment centers.• The neurotransmitters in the pathways

for emotional behavior include norepinephrine, dopamine, and serotonin.

The functions of the cerebellum include body balance and the planning and executing of voluntary movement.

• The vestibulocerebellum maintains balance and controls body movement.• The spinocerebellum enhances muscle tone and coordinates skilled,

voluntary movements.• The cerebrocerebellum plays a role in planning and initiating voluntary

movement.

Top

Frontofbrain

Corpus callosum

Cerebral cortex

Thalamus(wall of thirdventricular cavity)

Pineal gland

Cerebellum

Part of thelimbic system

Bridgethat connectsthe two halvesof the thalamus

Hypothalamus

Pituitary gland

Brain stem

Spinal cord

Brain stem

Cerebellum

Vestibulocerebellum

Spinocerebellum

Cerebrocerebelum

Unfolded

Regulation of muscle tone,coordination of skilled voluntary movement

Planning and initiation of voluntary activity

Maintenance of balance, control of eye movements

Vestibulocerebellum

Spinocerebellum

Cerebrocerebelum

Motor cortex

SpinocerebellumInformed ofmotor command

Makes adjustmentsas necessary

Motor commandto muscles

Informed ofactual performance

Activates receptorsin muscles and joints Movement Skeletal muscles

The brain stem is the medulla, pons, and midbrain.

• It is a vital link between the spinal cord and higher brain regions.– Most of the cranial nerves are

connected to the brain stem.– It has centers to control heart

and blood vessel function.– It plays a role in modulating

the sense of pain.– It plays a role in regulating

muscle reflexes involved in equilibrium and posture.

– The reticular formation ranges from the brainstem to the thalamus. It controls cortical alertness and direct attention.

– It has sleep centers.

Major Functions

1. Sensory perception2. Voluntary control of movement3. Language4. Personality traits5. Sophisticated mental events, such as thinking memory, decision making, creativity, and self-consciousness

1. Inhibition of muscle tone2. Coordination of slow, sustained movements3. Suppression of useless patterns of movements

1. Relay station for all synaptic input2. Crude awareness of sensation3. Some degree of consciousness4. Role in motor control

1. Regualtion of many homeostatic functions, such as temperature control, thirst, urine output, and food intake2. Important link between nervous and endocrine systems3. Extensive involvement with emotion and basic behavioral patterns

1. Maintenance of balance2. Enhancement of muscle tone3. Coordination and planning of skilled voluntary muscle activity

1. Origin of majority of peripheral cranial nerves2. Cardiovascular, respiratory, and digestive control centers3. Regulation of muscle reflexes involved with equilibrium and posture4. Reception and integration of all synaptic input from spinal cord; arousal and activation of cerebral cortex5. Role in sleep-wake cycle

Brain component

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem(midbrain, pons,and medulla)

Reticularactivatingsystem

Visualimpulses

Reticularformation

Brainstem

Ascendingsensory tracts

Descending motortracts

Spinal cord

Auditory impulses

Cerebellum

The spinal cord extends through the vertebral canal. 31 pairs of spinal nerves are connected to it.

• The cord ranges vertically from a large hole at the base of the skull.

• The attached spinal nerve pairs are:– eight cervical– twelve thoracic– five lumbar– five sacral– one coccygeal

The spinal cord consists of inner gray matter and outer white

matter.

The components of the reflex arc are:– 1.Receptor– 2.Afferent pathway– 3.Integrating center– 4.Efferent pathway– 5.Effector

• The receptor detects a stimulus (e.g., touching a hotplate).

• The effector makes the response of the reflex (e.g., withdrawal of the arm).

• The integrating center is within the gray matter of the spinal cord. Its neurons connect a given input (from the afferent pathway) to the proper output (from the efferent pathway).