Nervous SystemNervous System

Chapters 8 and 9Chapters 8 and 9

MIT Neuropathology PicsMIT Neuropathology Pics

Homeostasis ReviewHomeostasis Review Variables:Variables: Set Point:Set Point: Normal Range:Normal Range: SensorSensor: Detects change in internal : Detects change in internal

env’t. (sensory receptor)env’t. (sensory receptor) Regulatory CenterRegulatory Center: CNS- brain: CNS- brain EffectorEffector: muscle cell, gland cell or : muscle cell, gland cell or

specialized cellspecialized cell

System FunctionsSystem Functions Sensory Input: Sensory receptors within Sensory Input: Sensory receptors within

the skin and internal organs respond to the skin and internal organs respond to internal and external stimuli by generating internal and external stimuli by generating nerve impulses that travel to the brain and nerve impulses that travel to the brain and spinal cord.spinal cord.

Integration: The brain and spinal cord sum Integration: The brain and spinal cord sum up the impulses received from all over the up the impulses received from all over the body and send out nerve impulses.body and send out nerve impulses.

Motor Output: The impulses from the Motor Output: The impulses from the brain and spinal cord go to the effectors, brain and spinal cord go to the effectors, which are muscles and glands. which are muscles and glands.

Organization

Nervous TissueNervous Tissue

All nervous tissue is composed of only two All nervous tissue is composed of only two types of cells: types of cells: Nerve cells (neurons)Nerve cells (neurons) and and supporting cells (neuroglia).supporting cells (neuroglia).

Neurons vary in appearance, but all have Neurons vary in appearance, but all have 1) cell body, 2) dendrite, and 3) axon.1) cell body, 2) dendrite, and 3) axon.

Neurolemmocyte (Schwann cell): Neurolemmocyte (Schwann cell): specialized neuroglial cell of the PNS that specialized neuroglial cell of the PNS that creates myelin.creates myelin.

Types of NeuronsTypes of Neurons

Motor: impulses from CNS to Motor: impulses from CNS to muscles or glands (mostly muscles or glands (mostly multipolar).multipolar).

Sensory: impulses from sensory Sensory: impulses from sensory receptors to the CNS (many are receptors to the CNS (many are unipolar).unipolar).

Interneurons: impulses conducted Interneurons: impulses conducted within the CNS (often multipolar).within the CNS (often multipolar).

Motor NeuronMotor Neuron

Sensory NeuronSensory Neuron

InterneuronInterneuron

CNSCNS

Gray matter: cell bodies and short Gray matter: cell bodies and short nonmyelinated fibers.nonmyelinated fibers.

White matter: contains myelinated axons White matter: contains myelinated axons that run together in bundles called tracts.that run together in bundles called tracts.

Meninges: membranes covering the brain Meninges: membranes covering the brain and spinal cord. (dura mater (outermost), and spinal cord. (dura mater (outermost), arachinod, pia mater (innermost)).arachinod, pia mater (innermost)).

The subarachinod area is full of The subarachinod area is full of cerebrospinal fluid.cerebrospinal fluid.

CNS: Spinal CordCNS: Spinal Cord

Extends from the base of the brain Extends from the base of the brain through the foramen magnum of the through the foramen magnum of the cranium.cranium.

It is protected by the vertebral It is protected by the vertebral column and is located in the column and is located in the vertebral foramen. vertebral foramen.

The spinal cord ends at L1.The spinal cord ends at L1.

CNS: Spinal Cord AnatomyCNS: Spinal Cord Anatomy Central canal with gray matter surrounded by white Central canal with gray matter surrounded by white

matter.matter. The central canal contains cerebrospinal fluid.The central canal contains cerebrospinal fluid. Portions of sensory and motor neurons reside in the Portions of sensory and motor neurons reside in the

gray matter as do interneurons. The posterior root gray matter as do interneurons. The posterior root of a spinal nerve enters here and the anterior root of a spinal nerve enters here and the anterior root (containing motor fibers) exits the gray matter.(containing motor fibers) exits the gray matter.

Spinal nerves are created by the joining of these two Spinal nerves are created by the joining of these two roots (part of PNS).roots (part of PNS).

White matter is made of ascending and descending White matter is made of ascending and descending tracts that take data to and from the brain. Because tracts that take data to and from the brain. Because these tracts cross just after they enter or exit the these tracts cross just after they enter or exit the brain, the right side of the brain controls the left side brain, the right side of the brain controls the left side of the body and the left side of the brain controls the of the body and the left side of the brain controls the right side of the body.right side of the body.

CNS: Spinal Cord FunctionCNS: Spinal Cord Function

Communication between the Brain and the Communication between the Brain and the PNS.PNS.

Example: hand touched Example: hand touched sensory fibers sensory fibers generate nerve impulses generate nerve impulses passes passes through sensory neurons through sensory neurons spinal cord spinal cord ascending tract ascending tract brain. brain.

Center for reflex arcs. A stimulus causes Center for reflex arcs. A stimulus causes sensory receptors to generate nerve sensory receptors to generate nerve impulses through sensory nerves these go impulses through sensory nerves these go to interneurons that integrate the data and to interneurons that integrate the data and respond.respond.

CNS - BrainCNS - Brain

The brain is organized in ventricles. The The brain is organized in ventricles. The Cerebrum is in the two lateral ventricles, Cerebrum is in the two lateral ventricles, the diencephalon is in the third ventricle, the diencephalon is in the third ventricle, and the brain stem is in the fourth and the brain stem is in the fourth ventricle.ventricle.

Cerebrum: largest portion; last to receive Cerebrum: largest portion; last to receive sensory input and integrate it before sensory input and integrate it before commanding voluntary motor response; commanding voluntary motor response; coordinates other areas of the brain; and coordinates other areas of the brain; and carries out higher thought processes, carries out higher thought processes, memory, language, speech, and learning.memory, language, speech, and learning.

More BrainMore Brain Diencephalon: hypothalamus, thalamus Diencephalon: hypothalamus, thalamus

and the pineal gland. Thalamus receives and the pineal gland. Thalamus receives all sensory input except smell. This area all sensory input except smell. This area integrates this information and sends it to integrates this information and sends it to the appropriate area of the cerebrum.the appropriate area of the cerebrum.

Cerebellum: Receives sensory input from Cerebellum: Receives sensory input from the eyes, ears, joints, and muscles about the eyes, ears, joints, and muscles about the position of body parts. It also receives the position of body parts. It also receives information from the cerebral cortex as to information from the cerebral cortex as to where those parts should be located. where those parts should be located. Therefore it plays a role in posture, Therefore it plays a role in posture, balance, and coordination.balance, and coordination.

Even More BrainEven More Brain

Brain stem: contains the midbrain, the Brain stem: contains the midbrain, the pons, and the medulla oblongata. pons, and the medulla oblongata.

MidbrainMidbrain – relay station for tracts – relay station for tracts

PonsPons – contains bundles of axons traveling – contains bundles of axons traveling between the cerebellum and the rest of between the cerebellum and the rest of the CNS.the CNS.

Medulla OblongataMedulla Oblongata - contains a lot of - contains a lot of reflex centers for controlling heartbeat, reflex centers for controlling heartbeat, breathing, and vasoconstriction.breathing, and vasoconstriction.

PNSPNS

Composed of neurons and ganglia. Composed of neurons and ganglia. Ganglia are swellings associated with Ganglia are swellings associated with nerves that contain collections of cell nerves that contain collections of cell bodies.bodies.

Somatic division: serves the skin, Somatic division: serves the skin, skeleton, and tendons.skeleton, and tendons.

Autonomic division: regulates the Autonomic division: regulates the activity of cardiac and smooth activity of cardiac and smooth muscles and glands.muscles and glands.

Types of PNS NervesTypes of PNS Nerves

Cranial: 12 pairs; many belong to the Cranial: 12 pairs; many belong to the somatic division; includes the vagus somatic division; includes the vagus nerve which has branches to most of nerve which has branches to most of the internal organs.the internal organs.

Spinal: 31 pairs; associated with the Spinal: 31 pairs; associated with the 3 regions of the vertebral column; 3 regions of the vertebral column;

Somatic DivisionSomatic Division

Most actions are voluntary which Most actions are voluntary which means they originate in the cerebral means they originate in the cerebral cortex. cortex.

Others are reflexes: cranial (blinking) Others are reflexes: cranial (blinking) and spinal reflexes (hand on stove).and spinal reflexes (hand on stove).

Autonomic DivisionAutonomic Division

Sympathetic: most arise from the lower Sympathetic: most arise from the lower thoracic or lumbar region. Highly involved thoracic or lumbar region. Highly involved in the fight or flight reflex.in the fight or flight reflex.

Parasympathetic: Craniosacral; promotes Parasympathetic: Craniosacral; promotes all the internal responses we associated all the internal responses we associated with a relaxed state.with a relaxed state.

Commonalities: 1) they function Commonalities: 1) they function automatically and usually involuntary, 2) automatically and usually involuntary, 2) they innervate all internal organs, and 3) they innervate all internal organs, and 3) they utilize 2 motor neurons and 1 they utilize 2 motor neurons and 1 ganglion for each impulse.ganglion for each impulse.

Nerve ImpulsesNerve Impulses Resting Potential: membrane is polarized (outside Resting Potential: membrane is polarized (outside

+ inside -). The sodium potassium pumps are + inside -). The sodium potassium pumps are responsible for setting this up.responsible for setting this up.

Action Potential: 1) depolarization (inside +); 2) Action Potential: 1) depolarization (inside +); 2) repolarization (inside -).repolarization (inside -).

If an axon is myelinated, the action potentials are If an axon is myelinated, the action potentials are stimulated between the nodes of Ranvier (faster stimulated between the nodes of Ranvier (faster potential) in non-myelinated it stimulates another potential) in non-myelinated it stimulates another part of the axomembrane.part of the axomembrane.

All or None event. One way from cell body to All or None event. One way from cell body to axion terminal.axion terminal.

TransmissionTransmission

Every axon terminates in an axon Every axon terminates in an axon terminal. All of these lie close to a terminal. All of these lie close to a dendrite or the cell body of another dendrite or the cell body of another neuron.neuron.

Pre-synaptic and Postsynaptic region. Pre-synaptic and Postsynaptic region. Between them is the Synaptic cleft. Between them is the Synaptic cleft.

TransmissionTransmission Transmission is carried out by molecules called Transmission is carried out by molecules called

neurotransmitters. These are stored in vesicles neurotransmitters. These are stored in vesicles in the axon terminals.in the axon terminals.

Impulse reaches terminal Impulse reaches terminal opens calcium opens calcium channels channels Calcium enters the terminal Calcium enters the terminal vesicles move toward membrane for exocytosis vesicles move toward membrane for exocytosis neurotransmitters are released and diffuse neurotransmitters are released and diffuse through synaptic cleft through synaptic cleft neurotransmitters bind neurotransmitters bind with receptors on postsynaptic membrane.with receptors on postsynaptic membrane.

Depending on the neurotransmitter and Depending on the neurotransmitter and receptor the response will be excitation or receptor the response will be excitation or inhibition.inhibition.

IntegrationIntegration

Neurons can have many dendrites and can Neurons can have many dendrites and can synapse with many other neurons.synapse with many other neurons.

An excitatory NT produces a potential An excitatory NT produces a potential change called a change called a signalsignal. The signal drives . The signal drives the polarity of a neuron closer to an action the polarity of a neuron closer to an action potential. An inhibitory NT does the potential. An inhibitory NT does the opposite.opposite.

Integration is the summing up of all of the Integration is the summing up of all of the excitatory and inhibitory signals. Which excitatory and inhibitory signals. Which ever side wins determines if an Action ever side wins determines if an Action Potential will be transmitted.Potential will be transmitted.