The Nervous System Flashcards
What is homeostasis?
The body’s ability to maintain a stable internal environment despite external changes.
What is the central nervous system (CNS) composed of?
The brain and spinal cord.
What is the peripheral nervous system (PNS) composed of?
All nerves outside the CNS that connect the brain/spinal cord to the rest of the body.
What is the difference between somatic and autonomic nervous systems?
Somatic controls voluntary movements (skeletal muscles); Autonomic controls involuntary functions (organs, glands, smooth muscle).
What are the two divisions of the autonomic nervous system?
Sympathetic (“fight or flight”) increases heart rate and energy use, while parasympathetic (“rest and digest”) slows heart rate and promotes relaxation.
What is a reflex arc?
A fast, automatic response to a stimulus that bypasses the brain and is processed in the spinal cord.
What are the five steps of a reflex arc?
- Stimulus detected by receptors.
- Sensory neuron sends a signal to the spinal cord.
- Interneuron processes the signal.
- Motor neuron sends a response to muscles.
- Effector (muscle/gland) reacts (e.g., pulling hand away from heat).
Why do reflexes protect the body?
They reduce reaction time and prevent injury by responding instantly before the brain processes the danger.
What is sensory adaptation?
When sensory receptors stop responding to an unchanging stimulus (e.g., getting used to a strong perfume).
What are the four types of sensory receptors?
- Photoreceptors – Detect light (in the retina).
- Chemoreceptors – Detect chemicals (taste buds, olfactory cells).
- Mechanoreceptors – Detect touch, sound, and balance (skin, ear).
- Thermoreceptors – Detect temperature changes (skin, hypothalamus).
What is the role of proprioceptors?
Detect body position and movement in muscles, tendons, and joints to help with balance and coordination.
What are the three layers of the eye?
Sclera (outer) – Protects and maintains shape.
Choroid (middle) – Supplies blood, absorbs stray light.
Retina (inner) – Contains rods and cones for vision.
What is the function of the lens?
Focuses light onto the fovea centralis for sharp vision.
What is accommodation?
The lens changes shape to focus on near or far objects.
What do rods and cones detect?
Rods detect black and white, dim light; Cones detect color and bright light.
What causes the blind spot?
The optic disc, where the optic nerve leaves the eye, has no photoreceptors.
What are common vision disorders?
- Astigmatism – Irregular cornea, causing blurry vision.
- Myopia (nearsightedness) – Light focuses in front of retina.
- Hyperopia (farsightedness) – Light focuses behind retina.
What are serious eye diseases?
- Glaucoma – Increased eye pressure damages optic nerve.
- Cataracts – Clouding of the lens, blocking light.
- Retinal Detachment – Retina separates, causing vision loss.
- Macular Degeneration – Damage to fovea centralis, affecting central vision.
What are the three parts of the ear?
- Outer Ear – Collects sound (pinna, auditory canal).
- Middle Ear – Amplifies vibrations (eardrum, ossicles).
- Inner Ear – Converts vibrations into nerve signals (cochlea, hair cells).
How do we hear sound?
- Sound waves enter the ear canal.
- Eardrum vibrates and moves ossicles.
- Ossicles amplify sound and pass it to the cochlea.
- Hair cells in the cochlea detect movement and send signals to the brain.
What causes hearing loss?
- Nerve Deafness – Damage to cochlea’s hair cells (permanent, caused by loud noise or aging).
- Conduction Deafness – Blockage in outer/middle ear (earwax, infections, ossicle damage).
How does the ear help with balance?
- Semicircular canals detect head rotation.
- Utricle & Saccule detect tilt and gravity.
- Otoliths (tiny crystals) shift to stimulate hair cells, sending signals to the brain.
What are the main touch receptors?
- Light touch receptors – Detect soft contact.
- Pressure receptors – Detect firm touch/squeezing.
- Pain receptors (nociceptors) – Detect injury/damage.
- Thermoreceptors – Detect temperature changes.
What type of receptors are in taste buds?
Chemoreceptors detect dissolved food particles for sweet, sour, salty, bitter, and umami flavors.
How does smell work?
Olfactory receptors in the nasal cavity detect airborne chemicals and send signals to the olfactory bulb in the brain.
Why are taste and smell linked?
80-90% of taste perception comes from smell, which is why food tastes bland when you have a cold.
What is a neuromuscular junction?
The synapse between a motor neuron and a muscle where acetylcholine triggers muscle contraction.
What happens if the dorsal root of a spinal nerve is severed?
The body cannot detect sensory stimuli, so the reflex arc won’t be triggered.
What happens if the ventral root is severed?
The muscle won’t receive motor signals, so it can’t respond to stimuli.
Which type of neuron carries impulses toward the CNS?
Sensory neurons (afferent neurons).
What part of the brain controls balance, posture, and coordination?
Cerebellum.
What are the first and last elements in a reflex arc?
First: Sensory receptor, Last: Effector (muscle/gland).
How does a nerve impulse cross a synapse?
A neurotransmitter is released from the axon of the pre-synaptic neuron to the dendrite of the post-synaptic neuron.
What are the two divisions of the autonomic nervous system?
Sympathetic (“fight or flight”) & Parasympathetic (“rest and digest”).
A patient with a blockage at a sensory neuron’s entry point in the spinal cord can still move their hand but can’t feel pain. Why?
Sensory signals can’t reach the brain, but motor signals are unaffected.
Where does paraplegia occur?
At or below the T1 thoracic level, affecting the lower body.
Where does quadriplegia occur?
In the cervical region, affecting the arms, legs, and trunk.
Which part of the brain maintains homeostasis (hunger, thirst, body temp)?
Hypothalamus.
Which brain structure connects the left and right hemispheres?
Corpus Callosum.
What is the function of the thalamus?
Relays sensory information to the correct part of the brain for processing.
Which neurotransmitter is low in Parkinson’s disease?
Dopamine
How do drugs like Levadopa and Seligiline help Parkinson’s disease?
Levadopa replaces missing dopamine, while Seligiline prevents dopamine breakdown.
How do opiate drugs like heroin affect the brain?
They bind to mu and delta receptors, increasing dopamine and creating a euphoric effect.
What structure regulates how much light enters the eye?
Iris
Which eye disorder occurs when the cornea or lens has an uneven curvature?
Astigmatism
Which eye disorder is caused by an eyeball that is too long?
Myopia (nearsightedness).
Which disorder involves abnormal blood vessel growth in the retina, leading to vision loss?
Diabetic Retinopathy.
What structure in the ear is responsible for maintaining equilibrium?
Semicircular canals & vestibule (utricle and saccule)
Which ear structure helps equalize air pressure?
Eustachian tube
How does a cochlear implant help with hearing loss?
It bypasses damaged hair cells and directly stimulates the auditory nerve.
What happens to a neuron’s charge when an action potential starts?
Inside becomes positive (depolarization) as sodium (Na⁺) enters.
What happens to dopamine levels when cocaine is used?
Dopamine remains in the synapse longer, increasing its effects.
What happens in a sympathetic nervous system response?
Heart rate increases, pupils dilate, and norepinephrine is released.
What happens in a parasympathetic nervous system response?
Heart rate decreases, pupils constrict, and acetylcholine is released.
What is a synapse?
A small gap between neurons where nerve signals are transmitted chemically using neurotransmitters.
What are the three parts of a synapse?
Presynaptic neuron (sends signal), synaptic cleft (gap), and postsynaptic neuron (receives signal).
What happens when an action potential reaches the axon terminal?
Calcium (Ca²⁺) channels open, triggering neurotransmitter release into the synaptic cleft.
How do neurotransmitters cross the synapse?
They diffuse across the cleft and bind to specific receptors on the postsynaptic neuron.
What happens after neurotransmitters bind to receptors?
Ion channels open, triggering a response (excitatory or inhibitory)
How is the synaptic signal stopped?
Neurotransmitters are removed via reuptake, enzymatic breakdown, or diffusion
What is reuptake?
The presynaptic neuron reabsorbs neurotransmitters to stop the signal and recycle them.
What does acetylcholine (ACh) do at the neuromuscular junction?
It triggers muscle contraction by binding to receptors on muscle cells.
How do drugs affect synaptic transmission?
Some enhance neurotransmitter effects (e.g., cocaine blocks dopamine reuptake), while others inhibit them (e.g., Botox blocks ACh release).
How do SSRIs (Selective Serotonin Reuptake Inhibitors) treat depression?
They block serotonin reuptake, keeping more serotonin in the synapse to improve mood.
