Exam 2 Study Guide

What are the two divisions of the PNS? 

• Sensory- sends info to CNS through afferent neurons 

• Efferent- takes info from CNS to target cells via efferent neurons 

Neuron Function  

carry electrical signals

Dendrites Function

receive incoming signals 

Neuron Cell Body Function

control center 

Axon Function

carry outgoing signals 

What are interneurons, afferent neurons, and efferent neurons and their function?

• Main functional categories of nerve cells 

• Afferent: carry info from sensory receptors (eyes, skin, joints, etc) to CNS 

• Efferent: Carry info away from CNS to muscles and glands 

• Interneuron: middle-men messengers between efferent and afferent

What is a synapse? Differentiate between presynaptic and postsynaptic cells (relative to the synaptic cleft). 

• Synapse = region where an axonal terminal meets target cell 

• Pre-synaptic is sending cells. Post-synaptic is receiving cell

Name the types and functions of glial cells (only known functions discussed in the lecture). 

• Schwann cells (PNS) and oligodendrocytes (CNS): Wrap around axon and form insulating myelin sheaths 

• Satellite cells (PNS) = non-myelinating Schwann cell 

• Microglia (CNS) = specialized immune cells 

• Astrocytes (CNS) = several subtypes, multiple roles 

• Ependymal cells = one source of neural stem cells 

Which cells myelinate axons? 

Schwann (PNS) and oligodendrocytes (CNS) 

What is myelination? 

Process of wrapping an axon with myelin

What are the Nodes of Ranvier? 

Gaps in insulation

What are microglia?  

Specialized macrophage immune cells in CNS

On which side of the cell membrane are the following higher in concentration: Na+ and K+

- K+: inside the cell 

- Na+: outside the cell 

Compare graded potentials with action potentials. 

Graded Potential: Varied strength and used for short distance

Action Potential: very brief, large depolarizations for rapid signaling over long distances

Where on a neuron do graded potentials typically occur? 

dendrites of the cell body

Why are they called "graded" potentials?

Reflect stimulus strength

Why do graded potentials lose strength?

ions may cross membrane or electrical flow may be impeded

What is a cell's excitability? 

ability to fire an action potential

Where do action potentials occur in a neuron? 

The axon

• Where do action potential originate? 

The axon hillock

What is meant by "action potentials are all-or-none"?

There needs to be enough stimulus (>-55mV) to fire or no firing will occur

If they are all or none, how can we perceive different stimulation intensities?

By changing the frequency (how often the neuron fire)

Be able to describe in detail the events occurring in an action potential. To facilitate this, you may want to draw diagrams of each step and a plot depicting the change in membrane potential (mV) over time. 

Answer

Explain the changes in ion permeability and ion flow that take place during an action potential (e.g., Figure 8.9). 

During rest-high K+, depolarization: high sodium, repolarization: delayed increase in K+

Do you understand how the voltage-gated Na+ channel works (e.g., Figure 8.10)?

When at rest (rmp), the Na+ active gate is closed. Depolarizing stimulus arrives and active gate opens and Na+ enters cell. Inactive gate closes and Na+ entry stops. During repolarization caused by K+ leaving the cell, the two gates reset to their original positions.

How does depolarization progress in an action potential (e.g., Figure 8.13)?

Initial stimulus makes cell less negative to reach threshold that opens voltage gated sodium channels

How does conduction pass in an unmyelinated axon? How does it compare with a myelinated axon?

Unmyelinated: After axon hillock, Conduction reaches threshold and fire ap. Na+ influx depolarizes adjacent regions to threshold. Continuous conduction compared to jumping of myelinated

What is saltatory conduction?

Resistance of axon membrane to ion leakage out of the cell in myelinated axons

Describe absolute and relative refractory periods. 

Abs:Membrane cannot produce another AP Because Na+ channels are inactivated

Rel: When VG K+ channels are open, More difficult to depolarize to threshold

compare absolute and relative refractory periods. 

Absolute happens from start of ap depolarization to repolarization.

Relative: after hyper polarization as cell returns to resting potential

Where are neurotransmitters (NT) released from a chemical synapse? 

From the presynaptic terminal into synaptic cleft

How is the release of NTs triggered? Make sure you know step-by-step events, as discussed in the lecture.

(1) Open VG Ca2+ channels in bouton

(2)Ca2+ driven in by electro-chemical gradient

(3)After release of CA2+, Vesicles fuse with bouton membrane, Release NT by exocytosis

Why does the amount of NT released vary? 

Depends on the frequency of the action potential

When we say that "stronger stimuli release more NT," what does this mean? Moreover, how is it related to code duration and magnitude? 

Stimuli strength depends on frequency of APs. The longer and more intense (magnitude), the stronger the code that is delivered

When NTs are released across a synapse, they can impact the postsynaptic neuron by either exciting or inhibiting a cell. 

• What types of potential causes depolarization and hyperpolarization?  voltage change of the resting membrane potential.

Depolarization (EPSP): cell less negative, voltage closer to action potential threshold

Hyper-polarization (IPSP): cell more negative, voltage further away from action potential threshold

What is meant when we say that EPSP's and IPSP's summate (Figure 8.24)?  

Neurons add up all receiving signals to decide whether to send a signal or not

• Compare temporal and spatial summation. 

Spatial: EPSPs from different synapses occur on postsynaptic cell at the same time

One EPSP give multiple signals that occur close in time and sum before fading

• What happens when an IPSP dampens an EPSP? 

Reduced likelihood of neuron firing new action potential

Define Gray matter 

Gray matter conducts, processes, and sends info to body

Gray matter components:

Nerve cell bodies, dendrites, and axon terminals

Define White matter

Transmit nerve signals and connecting different areas of grey matter

White Matter component

Myelinated axons and tracts

Define Tracts

Axon bundles connecting CNS regions

Types of tracts and function

Ascending Tracts: Sensory information to brain

Descending Tracts: Motor signals from brain

Define nuclei

nerve cell bodies

What is cerebrospinal fluid? 

Salty solution that surrounds the brain

What is CSF produced by? 

Choroid plexus

What is the blood-brain barrier function?

Regulates movement between brain/cns and blood

What cells form in the BBB?

Endothelial cells supported by Astrocytes

What can cross the barrier?

Passes freely:Oxygen, CO2, small lipid molecules

Transporters: glucose

Where is the barrier reduced? Why? 

In circumventricular organs ,like the pineal gland, that need access to monitor blood, like circadian rhythm and pathogens

Explain how the Dorsal and ventral roots are organized in the spinal cord

Posterior (dorsal) horns: Contain visceral and somatic sensory nuclei

Lateral horns: Contain visceral motor nuclei

Anterior (ventral) horns: Contain somatic motor nuclei

What information do dorsal and ventral roots carry?

Ventral:carry motor

Dorsal: carry sensory

where does the information in dorsal and ventral roots come from, and where does it go for each neuron?

Ventral:carry motor info from CNS To muscles and glands

Dorsal: sensory information from body to spinal cord

Explain: Gray Matter = Dorsal, lateral, and ventral horns

Posterior (dorsal) horns: Contain visceral and somatic sensory nuclei

Lateral horns: Contain visceral motor nuclei

Anterior (ventral) horns: Contain somatic motor nuclei

What is the function of the pyramids in the medulla? 

Crossover/decussation: allows descending motor signals for voluntary movements to cross body

What is the function of the pons and midbrain? 

Relay station And Coordinates control of breathing

Midbrain function

Eye movement and Relay signals for: hearing and seeing reflexes

What is the function of the cerebellum? 

Process sensory information

Equilibrium and balance from somatic receptors

In the diencephalon, there are

centers for homeostasis. 

What does the thalamus do?

Relay Station integrating center for all sensory and movements signals before reaching cerebral cortex

What does the hypothalamus do?

Control of homeostasis

Center for behavioral drives

What do tropic hormones do? What is their target?

target other endocrine glands to stimulate the release of secondary hormones

What does the pineal gland do?

Melatonin, light and dark cycle, circadian rhythm

The pituitary is divided into two lobes called: 

Anterior pituitary and posterior

What are the eight major hormones of the anterior pituitary? Name and target tissues

• Thyroid-stimulating hormone(tsh): Thyroid hormones, thyroid growth

• Adrenocorticotropic (acth): Glucocorticoid secretion in adrenal cortex

• Follicle-stimulating hormone (fsh): Egg development, female sex hormones, Sperm production

• Lutenizing hormone (LH): Ovulation, Male sex hormones

• Prolactin: Breast development, Milk secretion

• Growth Hormone: – Bone and tissue growth, glucose metabolism, Movement of amino acids into cells

• Melanocyte: Stimulating Hormone: – Produces a darkening of the skin

• Endorphins: Neurotransmitters that affect pain pathways in PNS, Inhibiting perception of pain

Which of these anterior pituitary hormones are tropic?

Follicle Stimulating Hormone, Lutenizing Hormone, Adrenocortico Stimulating Hormone, Thryoid hormone

What is hypertrophy?What is atrophy?

Pituitary gland drives growth (hypertrophy) when overactive or atrophy (shrinking) when under active

Consider the functional areas of the cerebral cortex. Which lobe (or area if we discussed

specifics) is associated with each of the following, and what are their functions:

• Primary motor cortex

• Primary somatosensory cortex

• Primary visual cortex

• Primary motor cortex: frontal lobes. controls skeletal muscle activity on opposite side of body

• Primary somatosensory cortex: sensory areas in parietal lobe

• Primary visual cortex: occipital lobe. receives, process, stores visual info

Consider the functional areas of the cerebral cortex. Which lobe (or area if we discussed specifics) is associated with each of the following, and what are their functions:

• Primary auditory cortex

• Primary olfactory cortex

• Primary gustatory cortex

• Primary auditory cortex: temporal lobe. Receives, processes, stores auditory information

• Primary olfactory cortex: temporal lobe. Receives, processes, stores odor info

• Primary gustatory cortex: insula. Receives, processes, stores taste info

Define transduce

Conversion of a signal from one modality to another

What initiates membrane potential change?

a change in membrane permeability to ions (Na⁺, K⁺, Ca²⁺, Cl⁻), which drives ion movement and changes the membrane potential.

What is a modality?

Each receptor type responds to particular info

Sensory modality

Which sensory neurons activate and Where neurons terminate in brain

What are the two types of neural receptors? Are they myelinated?

Naked (myelin or no myelin) and complex- myelinated

What type of information do nonneural receptors receive?

Highly specialized cells associated with sensory neurons

Olfaction, gustation, vision, hearing/balance

Define:

• Adequate stimulus

Form of energy to which a receptor is most responsive

Define:

• Threshold

Minimum stimulus needed

Define:

• Receptor potential (graded potential)

Change in sensory receptor membrane potential

Define:

• Sensory Receptive field

Physical area where stimuli activates neuron

What are the four major groups of receptors?

Chemo, mechanical,thermo, and photo

What does it mean when we say "receptive field size determines sensitivity"?

less convergence of many primary neurons onto one secondary neurons lead to less sensitivity.

Smaller field = higher sensitivity, larger field=lower sensitivity

Know that sensory information travels to the brain via

ascending pathways or cranial nerves.

What are perceptual thresholds and habituation?

Stimulus level to be aware of sensation

Decreased perception through inhibitory modulation = habit

Understand that neurons determine

the sensory modality and where they terminate.

How does lateral inhibition help us distinguish a stimulus(see lecture figure)?

Enhances differences between strongest point of stimulus to its lower stimulus neighbor

What does lateral inhibition distinguishing stimulus do with primary, secondary, and tertiary neurons?

Primary neurons react to stimulus→ Secondary receiving strongest stimulus inhibits its neighbors→ Only Tertiary neuron synaptic cleft to secondary main neuron reacts

How is the intensity of a stimulus coded by the number of receptors activated and frequency (see lecture figure)?

Intensity of the stimulus Is determined by Number of receptors activated And Frequency coding, so more receptor and frequency means higher intensity

How do moderate and longer (and stronger) stimuli vary in duration and amplitude?

Stronger stimulus has longer duration and

How does stimuli strength variation change the frequency of action potentials and level of neurotransmitter release?

stimulus strength is encoded by → action potential frequency→ which controls how much neurotransmitter is released

Explain how tonic and phasic receptors adapt to a continuous stimulus.

Tonic-adapt slowly but does not stop (pressure, body position)

Phasic- rapidly adapt and turn off (changes like smell)

Trace the pathways for somatic sensation from the receptor to the somatosensory cortex (e.g., primary, secondary, and tertiary neurons)

Receptor → primary neuron (dorsal root ganglion) → synapse in dorsal horn → secondary neuron crosses in spinal cord → thalamus → tertiary neuron → somatosensory cortex.

What are nociceptors? Where are they located?

initiate protective responses and has free nerve endings

Found in: Skin, Joints, Muscles, Bones, Viscera

How is fast and slow pain different (in sensation and fibers)?

Slow pain: Dull/aching/more diffuse pain transmitted more slowly by unmyelinated C fibers (chronic)

Fast pain: Sharp and localized pain transmitted rapidly by myelinated 𝐴𝛿 fibers

What are examples of these nociceptors that each of the following respond to:

• Mechanical

• Thermal

• Chemical

– Mechanical (pinching, cutting)

– Thermal (extreme heat or cold)

– Chemical (acids, capsaicin)

Sort

CNS and PNS. PNS is motor and sensory. Sensory is somatic and visceral. Motor→somatic/autonomic. Autonomic→sympathetic/parasympathetic

Understand the division and functions of the efferent peripheral nervous system.

Autonomic:Smooth muscle, cardiac muscle, many glands, and some adipose tissue

Somatic Motor: skeletal muscles

Understand the division and functions of the efferent peripheral nervous system.

Autonomic:Smooth muscle, cardiac muscle, many glands, and some adipose tissue

Somatic Motor: skeletal muscles

Describe the two subdivisions of the autonomic division. How they can be distinguished anatomically and by their activity under certain situations.

Sympathetic: fight/flight. Short preganglion, long post. Thoracic and lumbar

Parasympathetic: rest and digest. Long pre, short post. Brainstem and sacral

How do autonomic reflexes support homeostasis, and which part of the brain controls these activities?

Sensory signals in and autonomic centers integrate and send out motor commands

Medulla and Pons controls: bp, respiration, bladder control

Hypothalamus: temp control, water balance, eating behavior