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Nervous System
Central Nervous System
Brain
● Made up of 5 vesicles
1. Telencephelon ● Cerebrum- the largest part of the brain and is comprised of 2 hemispheres ● Divided by the longitudinal fissure ● The left side of the cerebrum controls the right side of the body and vice versa ● The medullary body is the white matter of the cerebrum and consists of myelinated axons. ● White matter- Communication, connects different parts of the brain and spinal chord ● Covered in fatty substance called myelin ● Laterality- Some functions of the brain sits more on one side of the hemisphere than the other ● For example, a majority of us understand and comprehend language on the left hemisphere ● Cerebral Cortex - 1.5 mm outer layer of the cerebrum and is seat of consciousness ● Meaning to understand and comprehend information from everyday life is being delivered to the cortex ● Made up of gray matter ● Unmyelinated axons, cognitive functions, and movement
Cerebral cortex is divided into 4 lobes
● Frontal ● Primary motor cortex- where we consciously initiate movement, sends signals going down toward our motor neurons and our muscles ● Brocas area- located in the frontal lobe and is important in the production of speech ● Near the front of the lobe is the seat of higher understanding, consciousness, integration. Essentially where higher order reasoning takes place
● For example, knowing how to act in a specific situation, how to act socially amongst one person compared to another person ● Parietal ● Somatosensory cortex- receives signals coming up whether it's from the internal environment or the external environment ● It’ll pick up signals on touch, pain, temperature, pressure, vibration, proprioception, which is the body’s ability to sense its position without vision ● Occipital ● Processes visual images that come from our eyes, important for vision ● Temporal ● Responsible for memory/object recognition, processing sound and smell, and understanding language ● Under the temporal lobe is the insula which is important for taste
● Basal ganglia (parts)- Initiating and smoothing out motor activity, masses of gray matter ● For examples, if you wanna walk and move smoothly thats the basal ganglia ● If there's deficits in the basal ganglia, specifically dopamine (the neurotransmitter for this) its hard for people to initiate movement ● Limbic system (parts)- Important in emotion ● Consists of structures, Hippocampus (processes short term memory into long term memory). ● In charge of expression of instincts, drives and emotion.
2. Diancepehlon ● Thalamus- sorting/ relay center of the brain ● For example if someone were to tickle you the signals would go up the nerves in your arm, up the spinal cord,through the brain stem up to the thalamus, it would then go what is this signal and where should I send it to ● Hypothalamus - Master regulator ● Endocrine system ● Autonomic nervous system 3. Mesencephelon ● Midbrain 4. Metencephelon ● Pons ● Cerebellum- tone, balance, coordination ● Fine tunes information coming from the motor cortex
- Dura mater
- Tough layer
- Paper bag consistency
- Epi/extra dural space
- On top of this is where the skull is
- If the meninges become swollen its called meningitis
- Bleeding can occur in the spaces between the maters
- Extradural space
- Break bone
- Damaging meningeal arteries
- Extradural hematoma- bleeding is usually stuck to one particular area
- Subdural space
- Sub-Arachnoid space
- Subarachnoid hemorrhage - continues to bleed and spread trough
- Brain
Brain Stem
● Controls mainly involuntary functions, respiration, digestion, circulation, sleep patterns, hunger and thirst, heart rhythms and body temp, moving involuntary muscles, such as the heart ● Assists in regulating the CNS
3 Main Sections
- Midbrain (mesencephelon)
- Visual System
- Cranial nerves 3-
- Reflexes - Accomodation reflex- see an object then focus on the object - Pupillary light reflex- When both pupils constrict when you shine light into the eyes
- Subsatinan nagra
- Dopaminergic system
- Movement - branches to basal ganglia, initiating and smoothing out movement- Parkinson's resting tremour
- Behavior- Plays a role in motivation and the reward system by receiving dopamine
- Pons
- Cranial nerves 5-
- Connects different parts of the brain & helps control breathing & sleep
- Reflexes
- Jaw-Jerk reflex- if you open the jaw and stretch specific muscles, this would end up sending a sensory signal in to tell the motor neuron coming out to close the jaw
- Corneil-Blink reflex- when you rub your corneas both eyes blink reflexively
- Tensor Typani + Stapedius reflux- When you hear a very loud sounds they will retract and other incoming sound is dampened so you don't damage your ear
- Medulla Oblongota- Controls heart rate, blood pressures, and breathing
- Attaches to the spiral chord
- Cranial nerves 9- - Reflexes
- Swallowing + gag reflex
- Cough + sneeze reflex
- Reticular formation- Deep system of neurons with important and functional roles
- Nuclei sitting in the parts of the brain stem
- Midbrain nuclei
- Wakefulness, circadian rhythm
- Consciousness
- Pons and medulla
- Respiratory
- cardiovascular Damage in this area can cause people to go unconsciousness
- Divided into 31 pairs of nerves, 62 in total
- Named by where they are in the spine
- Divided into 5 groups, Cranial, thoracic, lumber, sacral, and coccygeal
- 8 pairs in the cervical region
- 12 pairs in the thoracic region
- 5 pairs in the lumber
- 5 pairs in the sacral region
- 1 pair in the coccygeal - Anatomy
- 2 nerve roots coming out of the spinal cord, connecting to a single spinal nerve
- Dorsal- back, sensory, info coming in
- Dorsal nerve root- sensory neuron comes through here, carriers sensory information
- Dorsal root ganglion- The bump is a bi polar body neuron since sensory neurons predominantly contain multiple axons
- Dorsal gray horn- where sensory information synapses
- Upper horn, skin and organs
- Mid horn, skin, organs, muscle
- Lower horn, proprioception- to now where you are in your own space
- Dorsal column medial lemniscus pathway - white matter between the horns
- fine touch, vibration, and proprioception- conscious
- Spinocerebellar pathway- straight from spine to cerebellum
- Unconscious proprioception
- Spinothallamic pathway
- Butterfly shaped area is all gray matter, where neurons speak to each other, where cell bodies are, synapses
- White matter is everything around it, carry axons up and down the brain, highways
- Ventral- front, motor, info from brain coming down
- 2 corticospinal tracts- cortex to spine
- Conscious limbs
- Conscious trunk
- 2 reticular spinal tracts
- Unconscious movement
- Ventral gray horn- gray matter
- Where motor signals synapses
- Motor neuron comes out the nerve root
- Lateral Gray horn
- Contains pre-synaptic sympathetic neuron bodies- autonomic nervous system( fight or flight)
- Sends automatic signals to everywhere to body
- This signal goes down the spinal ganglia- thoracic and lumbar region
Nervous tissue
- Neurons
- Excitable cells, when excited can perform an activity or function
- Sends signals and communicates
- Neurons don’t touch other neurons - Parts of Neurons
- Dendrites- receiving any incoming signals
- Soma- cell body
- All organelles will be in the soma
- Axon Hillick- Between soma and axon
Peripheral Nervous System
- Nerves pairs -Cranial nerves- 12 pairs -Cervical- 8 pairs -Thoracci- 12 pairs -Lumbar- 5 pairs -Sacral- 5 pairs -Cocygeal- 1 pair -Glia in PNS - Shwann cells - Makes one region of the neuron myelinated
- Satellite cells
- Myelinate and protect the cell body in the pns
- Ganglia- cell body in pns
Autonomic
- Automatic /Involuntry
- Sympathetic nervous
- Thoracolumbar - Heart
- Heart rate increases, pumps quicker to send more oxygenated blood to muscles
- Contraction increases, pumps harder for same reason - Respiratory
- Breathing rate increases, more oxygen into the cardiovascular system
- Bronchodilation, airways open up to allow more oxygen - Cardiovascular
- Peripheral blood vessels constrict, so it can direct more blood toward muscles, if you get cut you’ll be less likely to bleed out
- Muscle blood vessels dilate, so more blood gets redirected - Eyes
- Pupil dilation for increased peripheral vision - Parasympathetic
- Rest + Digest
- Craniosacral regions- Innovate structures that allow us to rest and digest
- Cranial nerve 3- pupils constrict
- Cranial nerve 7- Salivation
- Cranial nerve 9- Dif salivation
- Cranial nerve 10- Heart, airways, blood vessels - Heart
- Heart rate decreases, no point in wasting heart capacity and energy
- Contractile force decreases - Respiratory
- Respiratory rate decreases, since no point in wasting energy
- Bronchoconstriction, no need for big capacity since you’re resting - Cardiovascular
- Peripheral blood vessels dilate
- Muscles constriction - Eyes
- Pupils constrict
- Beta 2- relax, dilate, not release, tells airways to relax/ open up
- Beta 1 - Increase heart rate, and contractile force, kidneys increased blood pressure
- Alpha 2- stops neurons from sending to other
- Beta blockers
- Non specific, blocks beta 1 and 2
- Specific beta blocker, for example beta 1 reducing blood pressure, and slow heart rate
Action potential
- The resting membrane potential is at -
- As the neurotransmitter binds with the neuroreceptor the sodium pump opens increasing the action potential as the sodium goes into the neuron
- Every time the action potential hits -55 mV the voltage gated sodium pump opens in that area of the neuron
- Once the mv hits positive 30 the sodium channels close and the k+ channels open going ou the neuron
- Epilepsy- when the action potential of a neuron does hyper polarize resulting in neurons to keep misfiring
- To reset the neuron there are 3 na+ channels and 2 k+ channels
Synaptic Transmission
- As Na+ channels bring in sodium eventually it will cause the voltage gated calcium channels to open up releasing calcium into the neuron
- Then the calcium will stimulate the vesicles of the neurotransmitter, causing it to fuse with the plasma membrane releasing the neurotransmitter - If its excitatory it will open up sodium channels to begin the action potential - If its inhibitory it will open up chloride channels causing hyper polarization stopping the neuron to fire a signal
Neurotransmitters Overview
● Definition: Chemical messengers produced and released by neurons.
● Function: Can be excitatory (stimulate a response) or inhibitory (suppress a response).
● Release Site: Released into the synapse (gap between neurons).
● Targets: Bind to neurons, muscles , glands , or cells (effectors).
● Quantity: 100+ known neurotransmitters.
● Binding: Must attach to specific receptors on target cells to trigger effects.
⚡ 1. Acetylcholine (ACh)
● Receptors:
○ Nicotinic (excitatory)
○ α₂ (Alpha 2): Inhibitory — negative feedback to slow sympathetic output
○ β₂ (Beta 2): Inhibitory — bronchodilation (opens airways)
● Functions:
○ CNS: Triggers endogenous opioid release (reduces pain, anxiety).
○ PNS: Primary transmitters for sympathetic (fight-or-flight) responses.
b. Dopamine
● Receptors:
○ D₁: Excitatory
○ D₂: Inhibitory
● Functions:
○ CNS:
■ Reward & motivation
■ Motor control (via basal ganglia )
■ Parkinson’s Disease: Dopamine neuron death → tremors, rigidity, shuffling gait
○ PNS:
■ Regulates blood vessel diameter , GI motility , and kidney sodium excretion
😊 3. Serotonin (5-HT)
● Receptors:
○ Inhibitory: 5-HT₁, 5-HT₅
○ Excitatory: 5-HT₂, 5-HT₃, 5-HT₄, 5-HT₆, 5-HT₇
● Functions:
○ CNS: Controls sleep , mood , emotion regulation
○ PNS:
■ Regulates gut motility (too much → diarrhea)
■ Involved in bone remodeling (can strengthen or weaken bones)
🧩 4. GABA (Gamma-Aminobutyric Acid)
● Receptors:
○ GABAₐ and GABA_b
● Function: Main inhibitory neurotransmitter in the CNS.
● Mechanism: Increases Cl ⁻ ions into neurons → hyperpolarization → prevents firing.
● Clinical Relevance:
○ Drugs that enhance GABA are used for epilepsy and seizures (prevent overfiring).
