Chapter 11 The Nervous System BIO

Nerves

Macroscopic structure that contains bundles of neurons. Surrounded by connective tissues.

Cells found in the Nervous System ( Neurons )

Functional units of the nervous system

• Specialized cells to conduct electrochemical impulses→ regulates.

Cells found in the Nervous System ( Glial (Support) Cells )

Comes in many forms- each doing specific jobs to help support the function of neurons

• Ex: Schwan Cells that make myelin

Cell Body (soma)

Contains the nucleus and most of cytoplasm

• carries on the normal metabolic activities of the cell

• Integrates signals from dendrites and initiates nerve impulses down to the axon

Dendrites

Projection of the cell body

• numerous and highly branched

• Receive signals and send them toward the cell body

  • “The listeners”

Axon

Long single projection of cell body.

• Conducts impulses away from cell body towards terminal

• Can be anywhere from 1mm to 1m in length

Node of Ranvier

• Spaces between myelin sheath

Myelin Sheath

• Schwann cells → peripheral nervous system

A layer of fatty protein wrapped around sections of the axon

Synaptic Terminal

AKA axon terminal, synaptic bouton, and synaptic bulbs

• Releases neurotransmitters to communicate with other cells

Neurilemma

Thin outermost membrane of Schwann cells; helps to regenerate damaged PNS axons

• In the peripheral nervous system (PNS), Schwann cells make myelin

• Since there are no Schwann cell ins CNS, the myelin is made by other cells and therefore will not have a neurilemma and cannot regenerate damaged axons.

Sensory Neurons

Bring in sensory information from receptors to the CNS

Interneurons

Link neurons in the body, sensory to motor and interneurons to each other (connects messages and neurons to each other)

Motor Neurons

Relay information from CNS OUT TO the effectors (muscles or glands elsewhere in body )

The Reflex Arc

Simple neural circuits

• reflexes keep you out of danger- they are designed to be fast

• They are involuntary movement that are initiated without brain control.

  Sensory neurons-interneurons-motor neurons- muscle movement

Resting Membrane Potential (around -70mV)

At rest neurons is maintaining

• Sodium channels are closed (Na+ cannot get in)

• Potassium channels are closed (K+ cannot get out)

• Na+/K+ pump is active

Stimulus

Neurons stays the same until there is a stimulus

• Stimulus must be strong enough to Depolarize (make more positive) up to about -55mV for an action potential to occur. Known as threshold potential

Nerve impulse

A wave of positive charge traveling along the axon, resulting from the movement of ions across the axon membrane that results in the change of a membrane potential

Depolarization

Pump is deactivated

• An influx of sodium ions into the cell

• Makes the cell more positive

• Na+ in

Repolarization

Potassium K+ in

Pump still deactivated

• Potassium channels open making the cell more negative

• Does not close until the cell reaches -90 mV

The Refractory Period- Reseting the Neuron

-90 mV to -70 mV

• The neuron is NOT receptive to another stimulus until the resting potential of -70 mV and proper ion concentration (lots of Na+ outside and lots of K+ inside) are established

• Sodium-potassium pump ACTIVE

• Channels are closed

Neurotransmitters (NT’s)

Chemicals released by the presynaptic neuron that influence the activity of the postsynaptic neuron.

Presynaptic Neuron

1. Action potential reaches synaptic terminals causing Ca+ ions to flow into terminals

2. This causes synaptic vesicles inside terminals to fuse with the membrane freeing NT’s into synapse (cleft)

3. NT’s diffuse through synapse, bind to receptors on the dendrites of the postsynaptic neuron→ opens ion channels in dendrites

Postsynaptic Neuron

4. Depending on the type of ion channel opened, the dendrites becomes more positively charged (if Na+ flows into neuron) or more (if K+ flows out of neuron)

5. NT’s remaining in the synapse are degraded by enzymes, taken back in the presynaptic neuron through reuptake channels - The longer neurotransmitters are in the synapse; the greater the effect on the postsynaptic neuron

Responses in the Postsynaptic Neurons

Depending on the type of neurotransmitter excitatory vs inhibitory NT’s

Excitatory Neurotransmitters

• Open sodium channels in the postsynaptic neuron

• Sodium ions flow into the neuron causing local depolarization.

• Promotes nerve impulses by bringing potential closer to threshold

• Increase the likelihood of a response

Inhibitory Neurotransmitters

• Open potassium channels in postsynaptic neuron

• Potassium flows out of the neuron causing local hyperpolarization (neurons becomes more negative)

• Inhibits nerve impulses by bringing the potential further from the threshold

• Decreasing the likelihood of a response

Acetylcholine (ACh)

Neurotransmitter opens sodium channels in muscle fibers causing depolarization and muscles contraction.

Dompamine

Found in midbrain; helps control movement and also involved with the “pleasure centre”

Serotonin

Affects sleeps and mood

Endorphins

Natural pain killers in synapses in brain; also affects emotional areas of brain

Epinephrine/Norepinephrine

General excitatory neurotransmitter

Cholinesterase

Enzymes that degrades acetylcholine to end contraction, released by presynaptic neuron.

Skull

“Bony armor”

Meninges

3 layers of tough elastic tissue

Cerebrospinal Fluid (CSF)

Circulates between meninges and throughout brain and spinal cord

• Mainly for cushioning and shock absorption but also transports nutrients, hormones and white blood cells

Blood Brain Barrier

Protective barrier formed by glial cells and blood vessels

• controls entrance of substance into the brain from the blood

Medulla Oblongata (Hindbrain)

Controls autonomic functions such as breathing, blood pressure, swallowing

Pons (Hindbrain)

Relay (bridge) between left/right sides of cerebellum and relay to cerebrum

• responsible for controlling muscles for biting, chewing, and swallowing

Cerebellum (Hindbrain)

Coordination of unconscious and voluntary movements, balance and posture.

Midbrain

Role in eye movements and control skeletal muscles

• processes auditory and visual informations

Hypothalamus (Forebrain)

Releases hormones major link between nervous and endocrine systems.

Cerebrum (Forebrain)

Controls higher-level thinking→ Language, interpretation of sensory information, muscle movement.

Right of the brain

Controls the left side of the body, often specializes in artistic and spatial awareness

Left of the brain

Often specializes in logic, math, and language skills

Corpus Luteum

A band of myelinated axons that helps both sides of the brain communicate.

Frontal lobe

• Integrates info and control higher cognitive functions

• Reasoning, critical thinking, memory, and personality

• Controls precise, voluntary motor skills, including speech production

Parietal Lobe

• Process sensory info from skin

• Touch, pain, pressure, temperature

• Help process body position info

Temporal Lobe

Process auditory information, stores visual and verbal memory

Occipital Lobe

Process visual information.

Sensory Neurons

Carry information from the receptors to CNS

Motor neurons

carry information from the CNS to the effectors

Somatic Nervous system

Voluntary control

• controls mainly skeletal muscles (except vague nerve_> helps to control some organs)

Autonomic Nervous System

Involuntary control

• Control organs, glands, smooth muscles

• Maintain homeostasis (stable state) by stimulating or inhibiting involuntary process

• Controlled mainly by the medulla oblongata and hypothalamus

Sympathetic Nervous System

Fight or flight

• Prepares body for stressful or energetic activity

• Release epinephrine and norephinephrine

Parasympathetic nervous system

Rest and digest

• Dominates during times of relaxation

• Release acetylcholine