Unit 10 - The Nervous SystemCNS, PNS, and associated components

The Big PictureNervous system is divided into two main categories:

Central Nervous system (CNS): Brain and Spinal Chord

Peripheral Nervous system (PNS): Nerves to/from CNS

PNS is further divided into:

Somatic (SoNS): Connects the CNS to voluntary muscles

Autonomic (ANS): Regulates involuntary body functions

Big Picture Cont.Autonomic is further divided into:

Sympathetic (SNS): “fight or flight”

Parasympathetic (PSNS): “rest and digest”

Nervous System Flow Chart

CNSParts and Functions

The BrainThe main components of the brain include:

cerebrumcorpus callosumcerebellumthalamushypothalamuspituitary glandmedulla oblongatameninges

Cerebrum

Cerebrum ANATOMY

2 hemispheres

4 lobes (Frontal, Parietal, Occipital, Parietal) separated by sulci.

Cerebrum PHYSIOLOGY

Two hemispheres:

Right: creativity

Left: logic

Connected by the corpus callosum

CC is associated with integration of motor, sensory, and cognitive functions between the hemispheres.

Cerebrum PHYSIOLOGY

Sulci differentiate the cerebrum into 4 lobes

Frontal Lobe: Reasoning, Movement, Problem Solving

Parietal Lobe: Perception, Orientation, Recognition

Occipital Lobe: Visual processing

Temporal Lobe: Auditory stimuli, Speech, Memory

Cerebellum ANATOMY

“Little Brain”

Two hemispheres with a highly folded surface.

Cerebellum PHYSIOLOGY

Regulate eye movements

Coordinate limb movements

Maintain posture and balance

Motor decision making

ThalamusRelays sensory information from the body to the cerebral cortex.

HypothalamusInvolved in: homeostasis, emotion, thirst, hunger, circadian rhythms, and control of the autonomic nervous system.

Control of the pituitary gland

Pituitary Gland

“Master Gland” of the endocrine system

Under control of the hypothalamus

Pituitary Gland

Medulla Oblongata

Medulla OblongataControls involuntary functions such as:

Respiration

Heart Rate

Digestion

Relays higher level brain centers with the spinal chord.

Meninges

3 Layers

Dura Mater: outer layer closest to skullArachnoid Mater: provides cushioning effect for CNSPia Mater: attached to brain, contains capillaries

Subdural haematoma (btwn dura and arachnoid) resulting from traumatic event causes bleeding and inter cranial pressure and brain trauma

Remember...

The Peripheral Nervous System is composed of:

Sensory Neurons (Afferent Neurons)

Motor Neurons (Efferent Neurons)

What are these made of and how do they transport signals?

Parts of Neurons

Receive signals from other nerve cells

Covered in synapses

Parts of Neurons

Conveys electrical signals (range from 0.1mm to 2m)

Point of contact w/ cell body = Axon Hillock

Parts of Neurons

Carry out basic life functions of the neuron, including production of proteins and ATP.

Parts of Neurons

Protective covering of long Axons

Gaps btwn Schwann Cells are called Nodes of Ranvier

Sensory (Afferent) Neuron

Take information from sensory receptors to the CNS

Chemoreceptors are specific to the function they perform (taste, pain, etc.)

InterneuronAct as middle men between sensory and motor neurons

Reside completely within the CNS

Have many varieties and are multipolar (more than one dendrite)

Motor (Efferent) Neuron

Carry signals from CNS to effectors

Effectors can be glands or muscles as examples.

Signal Generation

Electrical activity is due to movement of ions past the cell membrane (Na+ and K+)

Neurons have an Electrical Charge Different from the Extracellular Fluid that surrounds them.  A difference in electrical Charge between Two Locations is called a POTENTIAL

Signal Generation RESTING POTENTIAL

Positively charged Na+ pumped out of cell, K+ “leak” out passively.

Causes a negative charge inside cell

Cell is now polarized and maintains this situation until stimulated.

Signal Generation THRESHOLD

Stimulation of the nerve is required to begin an impulse down the nerve

One sufficient stimulation occurs we can say that a THRESHOLD has been met

Once an impulse begins it can not be stopped, hence an “all or none” system is employed by neurons.

Signal Generation ACTION POTENTIAL

Stimulation of the nerve causes gates in the neuron to open.

Gates allow positive ions (Na+) to enter neuron causing the neuron to DEPOLARIZE.

Signal Generation ACTION POTENTIAL

After the impulse passes K+ gates allow K+ to leave cell

This causes REPOLARIZATION of the neuron.

Signal Generation ACTION POTENTIAL

This depolarization and repolarization is what we call an action potential or nerve impulse.

Signal Generation ACTION POTENTIAL

Na+/K+ pumps now return the respective ions to the proper side of the cell membrane

This is called the REFRACTORY period

No nerve signal can propagate during this period.

Signal Propagation MYELINATION

Axons that are myelinated propagate signals faster

Signals jump between the myelination (nodes of ranvier)

Speeds of 200 m/s can occur

The Synapse

Axons ends are slightly swollen and are called AXON TERMINALS.

These terminals transmit signals with dendrites, effectors (muscles) or receptors (sensors).

Small vesicles at the axon terminals contain NEUROTRANSMITTERS.

The Synapse NEUROTRANSMITTERS

Chemicals that are released into the synapse

Ex: Acetylcholine (ACh)

Join to receptors on neuron receiving the impulse

Cause membrane to become permeable to Na+ and a depolarization of the neuron

Threshold is met, and a signal propagates along the neuron.

Acetylocholinesterase rapidly breaks down ACh so that the chemical signal stops

Reflex Arc

Reflex ArcSensory neurons are stimulated and send a signal to the spinal chord

Interneurons relay the stimuli to motor neurons

Motor neurons send the signal to the effector muscles

The Brain does not receive a signal before the movement occurs and pain is not sensed until after the effector has been stimulated

SYMPATHETIC

Fight or Flight

Increases HR

Inhibits digestion

Dilates pupils

Vasoconstriction

Increases respiration

PARASYMPATHETIC

Rest and Digest

Pupil constriction

Promotes digestion

Controls resting HR

Relaxes muscles

ANS BRANCHES