Nervous System

Subdivisions

• CNS - central– Brain and spinal cord enclosed in

bony coverings

• Peripheral Nervous System– Nerve = bundle of nerve fibers in

connective tissue– Ganglion = swelling of cell bodies in

nerve

CNS

PNS

Brain

Cranial Nerves

Autonomic (involuntary) motor nerves

Somatic (voluntary) Sensory Nerves

Spinal Nerves

PNS

Spinal Cord

Fundamental Types of Neurons

• Sensory (afferent)– Receptors detect changes in body

and external environment– Information transmitted to brain or

spinal cord

• Interneurons (association neurons)– link sensory & motor pathways in CNS– 90% of our neurons are interneurons– Process, store & retrieve info

Fundamental Types of Neurons

• Motor (efferent) neurons– Send signals out to muscles and

gland cells– Organs that carry out responses

called effectors

Fundamental Types of Neurons

Fundamental properties of neurons

• Excitability (irritability) – Ability to respond to changes in the body

and external environment called stimuli

• Conductivity– Produce traveling electrical signals

• Secretion– When electrical signal reaches end of nerve

fiber, a chemical neurotransmitter is secreted

Neuron structure

• Cell body = perikaryon = soma– Single, central nucleus– Cytoskeleton of microtubules &

neurofibrils

• Vast number of short dendrites• Single Axon (nerve fiber) arising

from soma– Covered in Schwann cells

Schwann cells

• Myelin coated

• Neurilemma– Outer layer of SC– Brain/Spinal Cord do not have

• Nodes of Ranvier• Glia - “glue” that holds nerons together

a

Oligodendrocytes

• Hold nerve fibers together in the brain and CNS

• Make Myelin

Multiple sclerosis

• Myelin disorder– Myelin loss/oligodendrocyte damage– = demyelinization of white matter in

CNS– Hard, plaque-like lesions -->

inflammation– Nerve conduction impaired– More common women 20-40yrs

Nerves• Groups of peripheral nerve fibers

(axons) - like cables– Covered in myelin = look white

• Axons in CNS (tracts) = white matter• Gray matter - unmyelinated dendrites

and axons

Endoneurium -tissue that wraps axons

Fascicles - groups of wrapped axons

Perineurium - tissue that wraps fascicles

Epineurium - tough, fibrous sheath that covers whole nerve

Reflex Arcs

• 2 neuron arc: sensory & motor neurons– “Knee jerk”– Receptor of sensory neuron--> ganglion near

spinal cord --> motor neuron -->muscle

• 3 neuron arc: sensory, interneurons & motor neurons– “Withdrawal reflex”– Receptor of sensory neuron--> ganglion near

spinal cord --> interneuron --> motor neuron -->muscle

GANGLIONINTERNEURON

MUSCLE

RECEPTOR

MOTORNEURON

Divisions of the Brain

• Brainstem• Medulla oblongata• Pons• Midbrain

• Cerebellum• Diencephalon• Hypothalamus• Thalamus

• Cerebrum

http://www.youtube.com/watch?v=snO68aJTOpM

Brainstem

Brainstem

• Medulla oblongata• Enlarged, upward extension of spinal cord• Powers vital centers

• Cardiac, respiratory, vasomotor

• Pons• Works with medulla - complex reflexes

• Midbrain• governs basic behaviors like eating and

walking• Work with pons - sleep, arousal

Cerebellum

Cerebellum• Essential in normal movements

– Precise, smooth movements– Walking, drawing, hammering a nail

– processes input from other areas of the brain, spinal cord and sensory receptors to provide precise timing for movements

Diencephalon

• Hypothalamus– Impulses control glands, muscles, organs

• Heartbeat, intestines, vasomotory• ADH, RH

• Thalamus– Dumbbell-shaped– Produces sensations– Sensations with emotions– Arousal, alertness, activity

Cerebrum

Cerebrum

• Largest part of brain• Gyri - ridge• Sulci - grooves

– Fissure - deep sulci• Basal ganglia

– Gray matter in white matter– Automatic movements

Cerebrum• Corpus callosum -

connects left and right hemispheres

• Cerebral Cortex - layer of gray matter covering the cerebrum

Peripheral Nervous System (PNS)

• Made up of– Cranial nerves

• 12 pairs• conduct impulses from face/body to brain

– Table 9-2 p.921

– Spinal nerves• 21 pairs• Conduct impulses from body to spinal

cord

Peripheral Nervous System (PNS)

• Dermatomes - skin areas that map to a spinal cord region– Can use this

to detect region of cord injury

Peripheral Nerve Disorders

• Neuritis - inflammation of nerves• Sciatica - neuritis of sciatic nerve• Neuralgia - nerve pain• Bell’s palsy• Herpes zoster

Autonomic Nervous System

• From spinal cord/brainstem to tissue– Cardiac muscle tissue– Smooth muscle tissue– Glandular epithelial tissue

• Regulates involuntary functions– Heartbeat/intestines/gland secretions

Autonomic Nervous System

• Divisions of the ANS:

– Sympathetic nervous system• Emergency system: “fight or flight”

– Vasoconstriction, increased heart rate, decreased peristalsis

• Norepinephrine (NE)

– Parasympathetic nervous system• Normal daily functions

– Peristalsis, secretion of digestive juices/insulin• Acetylcholine (Ach)

Other Neurotransmitters

1. Action Potential2. Vesicles Fuse3. NT released4. NT crosses synapse5. Binds with receptors6. New Action Potential Fires7. Reuptake of NT

Nerve Impulse

Other NTs (are many more):• Dopamine• Epinephrine• Serotonin• Histamine

The venom contains 5% acetylcholine

Asian giant hornet

Organophosphate Poisoning

Disorders of the Autonomic Nervous System

• Stress-Induced Disease– Heart Disease (high blood pressure)– Digestive problems (colitis, ulcers)– Immunosuppression

• Neuroblastoma– Malignant tumor of Parasym. N.S.

• Usu in young children