Nervous System Notes

Neuron

The basic structural and functional unit of the nervous system, which transmits signals throughout the body.

• nerve CELLS and NOT nerves

• there main parts: dendrites, cell body, axons

Synapse

The junction between two neurons where signals are transmitted from one neuron to another.

Central Nervous System (CNS)

Consists of the brain and spinal cord; responsible for processing information and controlling behavior

• nerve impulses are received, interpreted, and co-ordinate responses

Peripheral Nervous System (PNS)

The nervous system outside of the CNS; connects the central nervous system to the limbs and organs

• cranial and spinal nerves

• voluntary (somatic), under conscious control

• involuntary (automatic), runs internal organs

Dendrites

The part of a neuron that receives signals from other neurons.

• highly branched

• conducts signals towards cell body

Axon

The long, thin part of a neuron that transmits signals away from the cell body/transmits signals to other cells

• “talker”

• often larger than the dendrites

• conducts signals away from cell body

Myelin Sheath

A protective layer around the axon that speeds up the transmission of nerve impulses.

Action Potential

A temporary reversal of the electric polarization of the membrane of a neuron; essential for transmitting signals.

Reflex Arch

The neural pathway that controls a reflex action, involving sensory neurons, interneurons, and motor neurons.

Epinephrine (Adrenaline)

A hormone released by the adrenal glands that increases heart rate and energy availability during stress

• source adrenal gland, centrail portion

• effects: “fight or flight” response

• increased heart rate, increase [glucose] in blood

• decreased blood flow to digestive track and skin

• increased breathing rate

• increased circulation to voluntary muscles

Inhibitory Neurotransmitters

Chemicals that decrease the likelihood of a neuron firing an action potential

• inhibit the firing of impulses

• can help stop responses such as tremors and seizures

• ex. serotonin, GABA

Excitatory Neurotransmitters

Chemicals that promote the firing of action potentials in neurons

• initiate impulses in adjacent (neighbouring) neurons

• ex. acetylcholine, norepinephrine, epinephrine, dopamine

• they get neurone firing (depolarization sequence)

Sodium-Potassium Pump

An active transport mechanism that pumps sodium ions out of a cell and potassium ions into a cell to maintain membrane potential.

Repolarization

The phase in a nerve impulse when the membrane potential returns to a negative value after depolarization.

Neurotransmitter

Chemicals used by neurons to communicate with each other.

Glial Cells

Supportive cells in the nervous system that assist with the maintenance and protection of neurons

• nourish nerouns, insulate the axon, speed of transmission

Negative Feedback Loop

A regulatory mechanism in which a stimulus causes an opposite output to maintain an optimal level.

Threshold Potential

The critical level to which a membrane potential must be depolarized to initiate an action potential.

Sensory neuron

carry information to central nervous system (electrical signals)

• input to spine

• transmit information from sensor to brain for processing

• long dendrite, short axon

Somatic Motor Neuron

• A type of neuron that transmits signals from the central nervous system to skeletal muscles, enabling voluntary movement.

• signals from spine outwards

• long axon, short dendrite

Automatic Motor Neuron

• A type of neuron that controls involuntary functions by transmitting signals from the central nervous system to smooth muscles and glands

• eg. digestive tract, cardiac muscle, glands

Sympathetic Nervous System

• flight or flight responses, eg. increased heart rate

What happens at each end of an axon

• each end of an axon transmit signals to another cell at a junction called the synapse

• The end of an axon releases neurotransmitters that bind to receptors on the next cell, facilitating communication.

Interneuron

• connect the sensory neuron to the motor neuron

• in the CNS

• for reflex: short axon, short dendrite

• to brain: short dendrite, long axon

Schwann cells

• form the myelin sheath

• protects and insulates herons

• speeds up the rate of transmission

Parasympathetic Nervous System

• maintains or establishes “normal” conditions in the body

• eg. decreases heart rate

Myelinated Nerve Fibers

• good insulators of nerves

• myelin formed from Schwann cells

• speeds up process of impulse transmission

Membrane Potential/Resting Potential

• not sending any signals

• between -60 and -80mv

Action Potential

• impulse as it moves along a neuron

describe the K+ and Na concentration

• K+ concentration highest inside the cell

• NA+ concentration highest outside cell how

how is the gradient maintained?

• maintained by the sodium-potassium pump

describe the use of energy to move K+ and Na+

• use of energy to ATP hydrolysis to actively move NA+ out and K+ in the cell

• 3Na+ and 2k+ moved at a time des

How are membrane potential voltages generated

• act net movement of +’ve or -’ve charge will generate membrane potential voltage

• gated ions channels will open or close in response to stimuli

Action Potential graph

• triggering the Na+ gates to open is an “all or nothing response”

• called threshold level of stimulation

Describe the 2 parts of the brain

• Cerebrum (conscious)

• the rest of the brain is unconscious

• right and left hemispheres with 4 surface lobes on each side

Thalamus

• relay between spinal cord and brain using the RETICULAR ACTIVATING SYSTEM

• screens sensory impulse

Cerebellum

• muscle coordinator and balance

Medulla Oblongata

• heartbeat

• respiration rate

• blood pressure regulation

• vomiting, coughing

Hypothalamus

• associated with hemostasis

• hunger, sleep, body temp/pressure

• contains the pituitary gland

Reflex Arch

• Travels via dorsal root (sensory neuron)

• moves to interferon in grey matter

• travels out via motor neurone in ventral root

• an automatic response

• brain processing is bypassed!!!fr

Frontal Lobe

• intellect

• voluntary muscles (skeletal)

Temporal Lobe

• hearing, smelling, speech Pa

Parietal Lobe

• sensory from skin o

Occipital Lobe

• vision Tr

Transmission and Impulses Across a Synapse Step #1

• electrical movement of signal ends at the axon bulb

• depolarization/repolarization events (Na/K+ ions) carry signals

Transmission and Impulses Across a Synapse Step #2

• movement of Ca2+ ions

• presynaptic membrane becomes permeable to Ca+

• Ca+ floods into axon bulb

• causes contractile filaments to shorten, vesicles drawn to membrane

Transmission and Impulses Across a Synapse Step #3

• Release of neurotransmitter

• neurotransmitter released through EXOCYTOSIS into synapse

• an ACTIVE process so ATP is needed

• mitochondria are often found is this region Transmission and Impulses Across a Synapse Step #1

Transmission and Impulses Across a Synapse Step #4

• movement across the synapse

• neurotransmitter diffuses across the synaptic gap

• moves from high to low concentration

• two important neurotransmitter

  • acetylcholine (arch) most common

  • noradrenalin (NA)

Transmission and Impulses Across a Synapse Step #5

• binding with receptors

• ARCH is recieved in post synaptic membrane by RECEPTORS

• “all or nothing” response

• remaining ARCH id synapse is cleared by enzyme

• ACETYLCHOLINE—ESTERASE x

Transmission and Impulses Across a Synapse Step #6

• ARCH binding to the receptors cause NA+ gates to open

• impulse continues along dendrite (electrically)

Nerve Impulse Transmission ZONE #1

• resting or membrane potential

• sodium on the outside, and K+ on the inside

• net negative charge inside vs outside

• THIS GIVES US -65MV

Nerve Impulse Transmission Zone #2

• depolarization, arrival at the impulse

• Na+ gates open—Na+ flood into the neuron (+40mv inside)

Impulse Transmission Zone #3

• repolarization

• Ka+ gates open—K+ moves out of the neuron

Re-establish the Resting Potential

• Na+ is moved out

• K+ is moved in

• this requires Na+/K+ pump, which requires ATP energy

What happens at 40mV

• threshold level must be reached before impulse is initiated

• “all or nothing response”

Nicotine

• shaped like ARCH (neurotransmitter)

• binds to receptors, increasing action potentials

• INCREASES dopamine release, excited

• stimulate muscle movement, breathing, heart rate, learning, and memory

Alcohol

• mimics GABA’s effect by binding to GABA receptors

• acts as an inhibitor

• stimulates endorphins (like GABA and serotonin) as a naturally produced pain killer

Marijuana

• chemical produced called THC

• binds to cannabinol receptors

• affects cerebellum, cerebral cortex, and hippocampus

Cocaine

• acts by blocking dopamine transporters (clear dopamine out of the synapse

• dopamine builds up in the synapse

• amplified signal to neurons = feelings of euphoria

Fentanyl

• similar to morphine (a pain killer), but 50-100x more powerful

• belong to opioid group of drugs

• increases dopamine levels

• dangerous forms of it being syntjezised in labs

• deaths associated with respiratory distresss

The adrenal medulla of the adrenal gland

Control: secretion of adrenaline by adrenal medulla controlled by hypothalmus

Signal Travels: via brain stem—spinal cord—sympathetic nerve fibres—adrenal medulla

The Pituitary Gland—Posterior Pituitary

• hormones: ADH, oxytocin

• ADH: results in kidneys retaining water

• oxytocin: causes contraction of the uterus during childbirth and milk production @mammatry glands

The pituitary gland—Anterior Pituitary

Hormones:

GH: growth hormones (whole body)

FSH & LH: teste/overy development

LTH (lactogenic hormone): develop mammary glands

TSH: thyroid stimulating hormone

ACTH: stimulates adrenal glands

Negative Feedback Loop: ADH Release

• stimulus: [water] decreases in blood= low blood volume

• sensor: hypothalamus

• organ: pituitary gland (posterior)

• response: release ADH—effect collecting duct of nephron (kidney)= water is reabsorbed into blood (remove original stimulus)

• homeostasis: retain water= blood volume increases

ONCE BLOOD [WATER] INCREASES, PATHWAYS IS SHUT DOWN=SELF REGULATORY

Negative vs. Positive Feedback

• ADH release= negative feedback (body responses bring you BACK to homeostasis)

• oxytocin release during childbirth=positive feedback

body responses AMPLIFY…starting stimulus and end point are entirely different