DAT: Nervous System

• functional unit of the nervous system

• Cell that receives and sends signals

• Uses glucose as main energy source

• Most mature neurons cannot divide

Neuron

• neuron’s cell body containing the nucleus that stores genetic info for the cell

• responsible for metabolic functions

• Produces all neuronal proteins and membranes

• Processes incoming signals

• Contains specialized organelles that help to maintain the structure of the neuron and supply energy to drive activities

Soma

Receiving information and transferring it to the cell body

Dendrites

Sends electrical signals away from cell body

Axon

• where action potentials are initiated.

• connects the soma to the axon

Axon Hillock

• fatty structures in the neuron is separated by the Nodes of Ranvier

• insulates axons and increases signal transmission speed

• action potential travel faster

Myelin Sheath

Make myelin in CNS

Oligodendrocytes

Make myelin in PNS

Schwann Cells

Nodes of Ranvier

Gaps between myelin segments where ion exchange occurs.

• Electrical signal jumps node to node

• movement of an action potential down a myelinated axon

• Much faster than continuous conduction

Saltatory Conduction

• Electrical signals neurons use to communicate

• Happen when there is a big change in membrane charge (neuron is depolarized and the threshold level is reached)

• Signal travels down the axon using ion channels

• Depolarization, repolarization, hyperpolarization

Action Potential

• MP = –70 mV

• Inside is negative (Removal of a positive charge from the intracellular space)

• Inside: low Na⁺, high K⁺

• Outside: high Na⁺, low K⁺

Resting Potential

• Active pump that moves 3 Na⁺ out and 2 K⁺ in to maintain resting potential.

• Removal of a positive charge from the intracellular space

Na⁺/K⁺ ATPase

critical voltage (-55 mV) needed to trigger depolarization.

Threshold Potential

• Na⁺ channels open, allowing sodium ions to enter and make the cell more positive

• process by which a neuron has sufficiently _ (become less negative) to trigger an action potential

Depolarization

K⁺ channels open, allowing K ions to exit, returning the membrane to negative.

Repolarization

• K⁺ channels close slowly

• MP drops below resting (~ –80 mV)

Hyperpolarization

• No AP possible

• Na⁺ channels are open or inactivated

• Occurs during depolarization + most repolarization

• upper limit of an action potential’s frequency

Absolute Refractory Period

• Occurs during hyperpolarization

• action potential can be triggered, albeit a large stimulus is necessary

Relative Refractory Period

All-or-Nothing Principle

action potential either occurs fully or not at all once threshold is reached.

Synapse

junction between two neurons where communication occurs.

neuron that sends the signal via neurotransmitter release.

Presynaptic Neuron

neuron that receives the signal via receptors on its membrane.

Postsynaptic Neuron

Synaptic Cleft

gap between presynaptic and postsynaptic neurons.

Neurotransmitter (NT)

Chemical messenger released from presynaptic vesicles into the synaptic cleft.

Synaptic Vesicles

Membrane-bound sacs that store neurotransmitters.

open when membrane voltage changes

Voltage-gated

Exocytosis

process of neurotransmitter release into the synaptic cleft.

open when a molecule binds

Ligand-gated

• Depolarization

• MP becomes more positive

• Moves closer to threshold

• Usually Na⁺ channels open

Excitatory Postsynaptic Potential (EPSP)

• Hyperpolarization

• MP becomes more negative

• Moves away from threshold

• Usually K⁺ channels open

Inhibitory Postsynaptic Potential (IPSP)

Summation

combined effect of multiple EPSPs and IPSPs at the axon hillock that determines firing.

• Main excitatory neurotransmitter in the CNS

• depolarizes neurons

• important for learning & memory

Glutamate

• Mood, attention, learning, reward

• located in brain

Dopamine

• Sympathetic neurotransmitters involved in “fight or flight” response.

• in ANS /endocrine

• excitatory

Epinephrine / Norepinephrine

• Excitatory neurotransmitter

• Released at neuromuscular junctions

• Triggers muscle contraction

Acetylcholine (ACh) 

• Main inhibitory neurotransmitter in the CNS

• slows neuron firing

GABA

Secondary inhibitory neurotransmitter in the spinal cord.

Glycine

• Neurotransmitter affecting mood, appetite, and sleep.

• located in brain

Serotonin

Acetylcholinesterase (AChE) 

• Enzyme on postsynaptic membrane

• Breaks down ACh

• Prevents prolonged muscle contraction

• Brain + spinal cord

• Processes information and coordinates responses

Central Nervous System (CNS)

• All nerves outside CNS

• Connects CNS to the body

• Carries:

  • Sensory input → CNS

  • Motor output → muscles, organs, glands

Peripheral Nervous System (PNS)

Forebrain (Prosencephalon)

Develops into telencephalon and diencephalon

Becomes the cerebrum.

Telencephalon

 Forms the thalamus, hypothalamus, and pineal gland.

Diencephalon

• Part of the brainstem

• Involved in:

  • Motor movement

  • Visual processing

  • Auditory processing

• Acts as a relay center

  • Sends visual & auditory information to higher brain regions

Midbrain (Mesencephalon)

Develops into the metencephalon and myelencephalon.

Hindbrain (Rhombencephalon)

Metencephalon 

Forms the pons and cerebellum.

Myelencephalon

Forms the medulla oblongata.

• Outermost layer of cerebrum

• Responsible for higher cognition

  • Thinking, planning, decision-making

• Divided into lobes with different functions

Cerebral Cortex 

• Decision making

• Planning

• Voluntary movement

• Personality

• Language production

Frontal Lobe 

• Sensory processing

• Body awareness (proprioception)

Parietal Lobe

• Hearing

• Language comprehension

• Smell

Temporal Lobe

Responsible for visual processing.

Occipital Lobe

• Coordinates:

  • Balance

  • Posture

  • Fine motor control

• Smooths and fine-tunes movements

Cerebellum

Brainstem 

• Connects brain and spinal cord

• Made of:

  • Midbrain

  • Pons

  • Medulla oblongata

Midbrain

Relays sensory and motor information.

• Acts as a bridge

• Relays information between:

  • Cerebral cortex

  • Cerebellum

Pons 

• Controls essential subconscious functions:

  • Breathing

  • Heart rate

  • Digestive activity

• Most critical for survival

Medulla Oblongata

Reticular Formation

 Regulates alertness and consciousness.

Limbic System

Network responsible for emotion, memory, learning, and motivation.

• Relay station

• Sends sensory info from spinal cord → cerebrum

Thalamus

• Regulates:

  • Hormones

  • Body temperature

  • Hunger

  • Heart rate

  • Autonomic functions

• Uses osmoreceptors to monitor blood solute levels

Hypothalamus

Hippocampus 

Converts short-term memory into long-term memory.

• Processes strong emotions

  • Fear

  • Anger

  • Pleasure

Amygdala 

Spinal Cord

• Relays sensory info to brain

• Can produce reflexes without brain input

• Carry information TO the CNS

• From senses → brain/spinal cord

• bring nerve impulses from sensory organs to the brain or spinal cord

• Examples: vision, hearing, taste, touch, smell

Afferent (Sensory) Neurons

• Carry signals FROM the CNS

• To muscles and glands

• Produce movement or action

• receives the stimulus from the brain

• stimulate target organs to respond to the stimuli

Efferent (Motor) Neuron

Meninges

Protective membranes around the brain and spinal cord

• Tough outer layer

• Contains venous channels

• Returns blood to heart

Dura Mater

• Web-like middle layer

• Holds cerebrospinal fluid (CSF) beneath it

Arachnoid Mater

• Thin inner layer

• Directly attached to nervous tissue

• Rich in blood vessels

• Helps with CSF production

Pia Mater

• External environment

• Skin, muscles, bones, joints

Somatic sensory

• Controls:

  • Organs

  • Glands

  • Smooth muscle

  • Cardiac muscle

• Two-neuron pathway

• Effect depends on neurotransmitter

Autonomic Nervous System

Detect mechanical pressure or distortion.

Mechanoreceptors

Detect pain stimuli

Nociceptors

Detect temperature changes

Thermoreceptors

Detect chemical stimuli like taste or smell

Chemoreceptors

Electroreceptors

Detect electrical or magnetic stimuli.

“Fight or flight” — increases heart rate, dilates pupils and bronchi, raises blood sugar.

Sympathetic Nervous System

“Rest and digest” — lowers heart rate, increases digestion, promotes relaxation.

Parasympathetic Nervous System

Vagus Nerve

Main parasympathetic nerve that regulates visceral organs.

Ganglion

Synapse site between neurons

• Cell body in CNS

• Releases ACh

• Synapses at ganglion

Preganglionic Neuron

Goes from ganglion → target organ

Postganglionic Neuron 

Sympathetic Ganglia

Short preganglionic, long postganglionic neurons; uses ACh then norepinephrine.

Parasympathetic Ganglia 

Long preganglionic, short postganglionic neurons; uses only ACh.

Collects sound waves.

Outer Ear 

Vibrates with sound waves

Tympanic Membrane (Eardrum)

Contains ossicles (malleus, incus, stapes) that amplify sound.

Middle Ear

Stapes 

Transmits sound to the inner ear through the oval window.

Transduces Sound & Balance

Inner Ear 

• Spiral, fluid-filled structure

• Converts vibration → nerve signals

Cochlea 

Semicircular Canals

• Detect head movement and orientation

• Filled with fluid

Taste Buds 

Contain receptor cells for taste.

Clear front surface; lets light in + begins focusing

Cornea

Colored part; controls pupil size

Iris

Regulates light entry into the eye.

Pupil

Clear, biconvex; fine-tunes focus on retina

Lens

Contains photoreceptors (rods and cones).

Retina