Nervous System

Chapter 9

Functions• Stimulate all movement

• Receive sensory input

• Store and integrate information

• Maintain homeostasis

Organization• Two main divisions:

1. Central Nervous System (CNS)

a. Brain and spinal cord

b. Command and sensory integration center.

2. Peripheral Nervous System (PNS)

a. All nerves that communicate with spinal cord and cranial region.

Nice concept map to review

with!

Nervous System Cells

Neurons:

carries the nerve impulses, mitosis not possible after reaching maturity

Neuroglial cells:

supports neurons, does not carry impulses, mitosis is possible

throughout lifespan

Neuron cell body

Neuroglial cell nucleus

Neuroglial Cells• Most abundant in CNS

• 5 Major Types:

1. Microglial – phagocytes, protection

2. Oligodendrocytes – forms myelin in CNS

3. Astrocytes – provide support & connection between neurons and blood supply

4. Ependymal cells – lines cavities (Ventricles) of brain & spinal cord, helps form CSF, ciliated

5. Schwann cells – forms myelin in PNS

Can you find two neurons in this picture? What division of the NS is being shown here? What neuroglial cell is not shown here and

why not?

Neurons• Large in size• Very high metabolic rate• Amitotic (no replacing after

destruction), no centrioles• Extreme longevity…over 100

yrs. possible• Cell structures:

- cell body, axon, dendrites, myelin sheath, nodes of Ranvier, nucleus, axon terminals, end bulbs, synapse(If myelinated, will have Schwann cells or

Oligodendrocytes attached to axon)

Basic Neuron Anatomy

Impulses move along a one-way path!

Dendrites

Cell body

Axon

Neurons Structural Differences

1. Bipolar – rare, found in retina of eye

2. Unipolar – afferent (sensory) PNS

3. Multipolar – majority of all neurons; most in brain are multipolar.

Neuron Organization

Neuron types: Sensory, Interneurons, Motor

Neuron Functional Differences

Integrates and coordinates info from afferent, sends out response to efferent

Neuron Pathway Types

**Be able to describe the difference between the pathways.

Nerve Impulse Nerve Impulse ConductionConduction

Neuron at Resting Potential

• Membrane is polarized (charged!)

• -70mv inside cell• Inside more negative

than outside.• What keeps it neg?

Large, negative proteins, chloride ions, and nucleic acids inside.

Leaky membrane allows Na+ and K+ ions to diffuse, so Na/K pump is

always working.

Moving Action

Potential

Animation

Action potentials are pulse-like waves of voltage.

Diffusion and electrochemical attraction move ions in/out

Myelinated axons increase speed of action potential.

Animation 2

Animation

Moving Impulse Along Neurona. Resting potential = -70mvb. Depolarization – reversal of

charges1. Na+ gates open and enters cell2. Potential changes to = +35mv

c. Repolarization – reversal of charges to restore resting pot.1. Na+ gates shut2. K+ gates open and leaves cell

d. Hyperpolarization – 1. Too much K+ moved out than was necessary

e. Refractory period – Fixing overcorrection with active transport. Cannot respond to another stimulus.1. Na/K+ pumps move Na+ out and K+ into cell to re-establish polarity

Animation 2

Animation 3

Synapse• Neurotransmitter

s: communication chemicals (50+ types known!)

• Threshold – minimum amount of stimulus needed for depolarization.

• Reuptake transporters recycle neurotransmitters.

Animation Neuron Communication Video

Neurotransmitters• Excitatory – Increases activity of

postsynaptic neuron.

• Inhibitory – Decreases activity of postsynaptic neuron.

More than one type of neurotransmitter can be released by a single neuron and one neuron can have synapses with several different neurons (convergence and divergence), thus, a single neuron can have receptors for many different types of neurotransmitters.

Common Neurotransmitters• Acetylcholine – Excitatory, skeletal muscle

contraction• Norepinephrine – Excitatory; increase HR.• GABA – Inhibitory, reduces anxiety.• Glutamate – Excitatory, involved in learning

and memory.• Endorphins – Inhibitory, natural opiates.• Serotonin – Involved in regulating

attention, emotions, mood disorders• Dopamine – Contributes in voluntary

movement; feel good emotions, Parkinson’s

Drug Effects on Neurotransmitters

• Pain killers – stop the release or block receptor sites or increase threshold.

• Caffeine – lowers threshold at synapses so neurons are more easily excited.

• Zoloft/Prozac/Paxil– keeps serotonin in the synapse longer; anti-depressants

• Dilantin – increasing effectiveness of ion transport; treats seizures

Go to Mouse Party for the affects of illegal drugs on neurotransmitters…

The BrainSections 9.11 and 9.13

* Contains approximately 100

Billion neurons

* Weighs about 3 pounds

Meninges: The Coverings

• Three Layers:1. Dura mater – outermost, tough, white2. Arachnoid mater – middle, web-like, CSF in subarachnoid space3. Pia mater – innermost, very thin on top of brain tissue

Meningitis: Inflammation of the meninges and CSF; typical causes are bacteria or virus; spinal tap needed to diagnose

Get your vaccination before college!

Cerebrospinal Fluid - CSF• Clear and colorless• Circulates within the

ventricles and sub-arachnoid space throughout CNS.

• Produced by the ependymal glial cells.

• Provides cushioning, optimum chemical environment, and nutrient/waste exchange.

• Hydrocephalus – too much CSF, blockage usually the cause, can cause neuron damage.

Hydrocephalus

Major Brain Structures• Cerebrum- Divided into 4

lobes:(frontal, parietal, occipital, temporal)

• Diencephalon:(thalamus, hypothalamus,

epithalamus)

• Brain Stem:(midbrain, pons, medulla oblongata)

• Cerebellum

Cerebrum

• Two cerebral hemispheres• Longitudinal fissure separates hemispheres. • Surface area increased with Gyri (ridges) and

Sulci (creases) or Fissures (deep grooves).• Connected by the Corpus Callosum• Function: Intelligence, memory, learning• Cerebral cortex – gray matter, outermost, all

conscious thinking occurs here• Olfactory bulb – sense of smell

Parieto-occipital sulcus

Functions of the Cerebrum

Prefrontal Cortex Problem Solving, Emotion, Complex Thought

Motor Association Cortex Coordination of complex movement

Primary Motor Cortex Initiation of voluntary movement

Primary Somatosensory Cortex Receives tactile information from the body

Sensory Association Area Processing of multi-sensory information

Visual Association Area Complex processing of visual information

Visual Cortex Detection of simple visual stimuli

Wernicke's Area Language comprehension

Auditory Association Area Complex processing of auditory information

Auditory Cortex Detection of sound quality (loudness, tone)

Broca's Area Speech production and articulation

Let’s Probe the brain! – find out how scientists found out where primary motor functions are.

Comparing Human, Dog and Rat Brains

DiencephalonMain structures: 1. Thalamus – main relay

station for sensory impulses (except smell) to the cerebral cortex.

2. Hypothalamus – regulates visceral movement (BP, GI tract, HR), body temperature, water and electrolytes, hunger, thirst, stimulate pituitary, maintains sleep and wake patterns.

3. Epithalamus – contains the Pineal gland which regulates biological clock.

Brain StemThree sections:1. Midbrain – visual and

auditory reflex centers, main motor pathway

2. Pons – “bridge”, relays impulses between: a. medulla/cerebrum b. cerebrum/cerebellum

3. Medulla Oblongata –regulates heart rate, blood pressure, respiration, coughing, sneezing, vomiting, swallowing

Cerebellum

• 2nd largest part of brain• Controls muscular

coordination• Maintains posture• Allows for smooth,

refined movements• Involuntary once

learned

Brain Disorders and Diseases

Common Brain Injuries

• Concussion – abrupt, but temporary loss of consciousness from a blow to the head.

Symptoms: headache, confusion, memory loss, lack of concentration

• Contusion – bruising of the brain due to trauma, leaking capillaries, commonly follows a concussion. Pia mater torn.Signs: Immediate loss of consciousness, loss of reflexes, decreased

blood pressure, cessation of respiration.

• Laceration – tear of the brain, large vessel rupture, cerebral hematoma, increased intercranial pressure.

Brain Tumors

Brain Aneurism

Cerebral thrombosis video

Strokes

Injury Effects

Phineas Gage

Man who survived a terrible brain injury in the 1800’s. First opportunity for scientists to study the frontal lobe and limbic system connection. Limbic system is the emotional region and frontal keeps the limbic region in control.Injury re-enactment video

cdnuolt blveiee taht I cluod aulaclty uesdnatnrd waht I was rdanieg. The phaonmneal pweor of the hmuan mnid, aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be in the rghit pclae. The rset can be a taotl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Amzanig huh? yaeh and yuo Iawlyas tghuhot slpeling was ipmorantt!

CAN YOU READ THIS?

The Spinal Cord

Conus medullaris

Cauda equina

Spinal Cord• Functions – to conduct nerve impulses and

serve as the center of spinal reflexes.• Anatomy of the spinal cord:

1. Ascending tracts – from sensory to brain

2. Descending tracts – from brain to motor

3. Composed of gray and white matter.4. Central canal contains the CSF.

5. Conus medullaris – end of cord at L16. Cauda Equina – cord fans out into nerves.

Nerve structure of the arm

31 pairs of spinal nerves

– Cervical– Thoracic– Lumbar

– Sacral

(What body regions do these nerves connect with?)

Dermatome Map

Check skin sensations to see what nerve has been damaged.

Paraplegia – injury below T1

Quadriplegia – injury above T1

Cross-Section of Spinal Cord

Afferent impulses travel through dorsal root to cord.

Efferent impulses travel through ventral root to effector.

Cross-section of Spinal Cord

Orientation of grey and white matter is opposite of the brain.

Grey matter = cell bodies

White matter = myelinated axons

• Rapid, automatic responses to specific stimuli.• Their purpose is to preserve homeostasis.• Little variability in the responses.• Only a few neurons are needed.• “Wiring” of a single reflex = “Reflex Arc”• Testing somatic reflexes can be used for

diagnostic purposes.• Examples: swallowing, sneezing, vomiting,

and knee jerk.

Reflexes

Reflex Classification

Stretch Reflex: “Patellar reflex”

Muscle spindles = sensory receptors involved in stretch reflexes

Innate Reflex: “Withdrawal reflex”

Lumbar Puncture or Spinal Tap

Needle inserted between 3rd and

4th lumbar vertebrae.

Epidural

Epidural given outside of the dura mater.

Herniated Vertebral Disc

Sciatica

• Compression and/or irritation of a sciatic nerve root or the sciatic nerve itself.

• Symptoms: pain or numbness in back, buttock, and/or parts of the leg and foot

Spinal Tumor and Herniated Disc

Peripheral Nervous System

Sections 14 and 15

READ TONIGHT!!!

Peripheral Nervous System

PNS

Sensory(Afferent)

Motor(Efferent)

SomaticSomatic

(Voluntary)Autonomic

(Involuntary)

Skeletal Muscles Sympathetic Parasympathetic

Visceral

Skin and special senses

General Info

All nerves that branch off the CNS and connect to other body parts.

• Cranial nerves – 12 pairs

• Spinal nerves – 31 pairs

Functions:1. To receive stimulus input and send to

CNS. 2. To relay the response from the CNS to

the appropriate effector organ.

Nerve Anatomy

Afferent or Sensory Nerves

1. Picks up stimuli from:

a. internal environment – visceral nerves

b. external environment – somatic nerves

2. Sends to CNS for interpretation

3. Typically unipolar or bipolar neurons

Somatic nervous system

– All voluntary or conscious activities

– Nerves connect to skeletal muscles

– Pathways have one motor neuron to muscle cells.

– Neurotransmitter: Acetylcholine

Autonomic nervous system

- All involuntary or unconscious activities.- Maintains internal environment- Nerves connect to cardiac, smooth

muscle or glands- Pathways have two neurons synapsing at

a ganglia before effector.- Neurotransmitters: Acetylcholine or

norepinephrine- Two divisions counterbalance each other:

Sympathetic and Parasympathetic

Comparing Motor Neurons

Sympathetic• prepares for energy-expenditure,

excitement or stressful situations• "fight" or take "flight“.• Nerve fibers originate from the thoracic

and lumbar regions of spinal cord.• Short Pre and Long postganglionic fibers

Parasympathetic

• Stimulated during calm and relaxing situations

• "rest" and "digest" .• Nerve fibers originate from the brain and

sacral region.• Long preganglionic fibers and short post

Which pathway is responsible here?

Sympathetic or Parasympathetic

Division of the ANS are distinguished by:

1. Unique origin sites

a. Sacrocranial vs. Thoracolumbar

2. Different lengths of their fibers

a. Preganglionic (long – Para, short – S)

b. Postganglionic (long – S, short – Para)

3. Location of their ganglia

a. P – close to effector

b. S – close to spinal cord