Bio 319- exam 3

Local cell to cell comm.: Gap Junctions

• Connect cytoplasm of 2 cells

• Proteins on the outside of cells- cells need to be specialized

• Efficient

• Only works if cells are physically touching

• Selective

Local cell to cell comm: Contact Dependent communication

• Two cells come together f

• Need cell receptor

• Common in the immune system

• Only works if cells are physically touching

Paracrine Secretion

• A cell releasing a signaling molecule and a different cell picking it up

• Short distance

• Common for immune system

Autocrine secretion

• A molecule that is excreted and then binds to the cell itself

• Common for immune system

Location communication often relies on diffusion of the signaling molecule

Diffusion is most suited for short-range communication

Long distance communication: Hormones

• Endocrine communication

• Hormones are released by endocrine cells

• Hormones are released into blood stream

• Bloodborne transport enables relatively quick transport throughout the body (minutes to seconds)

• Specifically can be sustained for long periods

• Intensity is signaled by number of molecules

• Reaches every cell in the body

Long distance communication pathways: Neurons

• These cells are long and thin

• Neurons use electrical impulses to communicate

• Axons propagate the electrical signal

• Synapses signal to target cell using transmitters

• Electrical signals travel very fast

• Each neuron only targets a limited number of target cells

• Intensity is encoded by firing frequency

• Energetically costly

Long distance communication: Neurohormones

• These are neurons that release hormones

• Body uses this when necessary

• Intensity comes from how many action potentials are released

Ionotropic receptors

• Ion channel

• Ligand binding opens channel

• Change in voltage

• Fast (milli second)

• Weak

Receptor Enzyme

• Slower than Ionotropic but faster than metabotropic

• Activates proteins

• Activate chemistry

Metabotropic receptors aka G protein coupled receptors

• Second messender receptor

• All activate an intracelluar pathway

  • Ion channels opening

  • Activation of a protein

  • DNA binding

• Relatively slow (seconds-hours)

• Effects are strong

Cytosolic and Nuclear receptors

• DNA binding —> transcription—> making more or less protein

• Slow (hours to days)

• Strong effect (can create a whole bunch of new proteins)

Ligands: Agonists

Activate a receptor

Ligands: Antagonists

Inactivate a receptor. Body uses both kinds

1. Competitive: Bind to a agonist but can be overruled

2. Non-competitive: Binds to another site but still inactivates the receptor

Canonical mammalian endocrine glands

• Hormones can be released by non-canonical tissues

• Endocrine tissues are specialized to release hormones

• Negative feedback loops control hormone levels

Hypothalamic-pituitary systems coordinates many hormonal systems

• The hypothalamus functions as a homeostatic integrator for many physioogical variables including many hormones. They are regulated by the hypothalamus and are typically regulated via the pituitary gland.

Pituitary

Master endocrine gland

• Controlled by hypothalamus

• Anterior pituitary (endocrine tissue)

• Posterior pituitary (neuronal tissue)

Posterior pituitary

• Directly releaes hormone, oxytocin and vasopressin, into the bloodstream.

  • Oxytocin: stimulates milk production in the mammillary glands and stimulates uterine muscles during labor

  • Vasopressin: enhances retention of water by the kidneys

• Neurohormonal release

• Cell bodies in hypothalamus

• Hormonal release in posterior

Anterior pituitary

• Hypothalamus signals the release of hormones from the anterior pituitary by secreting releasing hormones—> releasing hormones typically cause the release of secondary hormones —> activates a final effector hormone in pathways

• Portal vein blood vessels

• Releasing hormone from hypothalamus

• Secondary hormone released from ant. pit.

Hormones can have different effects depending on the receptors on the target tissue

• Alpha receptors impacts smooth muscle cells —> less blood flow into GI tract and kidneys

• Different in receptors leads to different intercellular responses

Neuronal Sympathetic signals

• Quick response- neural

• Intermediate- Hormones

• Chronic- Steroids

• Hormone is a back up to neuronal and can reach all the cells in the body

• Steroids are hydrophobic, bind to nuclear receptors (bind to DNA and changes DNA transcription- long term response)

Sex hormones shape sexual development

• Start with 2 ducts: male and female

• Later genetics decides between male and female

• Release of testosterone for males

  • Absence of male hormones leads to female

Neurons actively regulate ion concentration inside the cell

• The cell membrane separates the intracellular space from the extracellular space

  • Cell membranes, by themselves, are impermeable to ions

  • Electrically charged ions such as Na+, K+, and Cl- can only cross the membrane through ion channels. Ions can only pass through channels that are specific for that ion

Graded Potential

Are local changes in membrane potential that occur in varying degrees of magnitude or strength. Graded potentials are the result of changes in the permeability of the cell membrane to ions

Depolarization

A change in membrane potential that makes the membrane less polarized (less negative) than at the resting potential

Hyperpolarization

A change in membrane potential that makes the membrane more polarized (more negative) (-70 to more negative)

Repolarization

The membrane returns to its resting potential (returns to -70mV baseline)

Action potentials

• Brief, rapid, and large depolarization of the membrane potential

• Membrane potential becomes positive

• Opening of voltage gated channels

• All or nothing event

• Moves along membrane of axon without losing strength

Trigger Zones

• Most neurons

  • Trigger zone is located in axon hillock

• Sensory neurons

  • Trigger zone is located at intersection between dendrites and axon

Refractory Periods

Following an action potential, that area of the membrane cannot immediately fire another action potential. Functionally, this refractory period prevents reversal of an action potential and means that action potentials always move away from the Trigger zone

Graded Potentials

• Graded potentials are local changes in membrane potential (up or down) induced by stimulations

• Graded potentials die out over short distances and over time

• Graded potentials are additive, so multiple stimulations can come together result in a more pronounced or less pronounced effect

Integration of graded potentials

• Depolarizing stimuli

  • Excitatory postsynaptic potential

  • Example: Glutamate

• Hyper polarizing stimuli

  • Inhibitory postsynaptic potential

  • Example: Gaba

  • Further from potential

Integrating Signals

• More negative towards the axon hillock —> so probably going to be inhibited

• The further away from the trigger zone the less likely it is to fire the action potential

• Whatever happens closer to the axon hillock is what is going to happen

Propagated Signals

• There is a change in voltage

• Have a voltage gated channels - can open

  • Dramatic depolarization

What does a propagating action potential only travel down an axon in one direction?

• Action potentials can only move in one direction

  • This is because of the absolute refractory period

Two factors dictate the velocity with which an action potential travels down an axon

1. Axon diameter

2. Myelination

• Thicker diameter the faster it moves

Chemical synapses

Most neurons are not in direct, physical contact; instead, cells communicate across a small space called a synapse. The cell preceding is called the presynaptic cell and the cell receiving information is called the postsynaptic cell. In a chemical synapse, the presynaptic cell releases small molecules called neurotransmitters into the synapse. These neurotransmitters bind to the receptors on the postsynaptic membrane.

Electrical synapses utilize gap junctions instead of neurotransmitters

Electrical communication between distinct cells result in faster communication between cells, however, this communication does not allow for summation or integration of information across cells.

How is an action potential potential converted to a chemical signal?

Prior to release, most neurotransmitters are stored in membrane bound vesicles in the nerve terminal. When an action potential arrives at a presynaptic axon terminal, a sequence of events causes release of neurotransmitter to the postsynaptic cell

Cerebrospinal fluid

• Made from blood plasma

• Protects against skull

• Flows through ventricles in the brain

Ependymal

Line in the ventricles of the brain, they are very good at letting things in/keeping things out of the brain

Astrocytes

• Provide mechanical support for neurons in the brain

• Provide metabolic support for digesting waste

Microganglia

Acts as immune invader responds inside the brain

Oligodencytes

Cells that form the myelin sheaths for axons

Blood brain barrier

• Serves as a barrier to prevent contaminants from entering the brain

• Barrier is unique because all material moving into the brain NEEDS to be actively transported

Brainstem

• Evolutionary oldest part of the brain

• Regulates basic functions

  • Like, breathing, blood pressure, pain modulation, muscles reflexes, and arousal

Thalamus

• Relay system connecting different parts of the brain; consists of many small nuclei

Hypothalamus

• Communication between brain and body

• Receives input from body

• Homeostatic integrator

Cerebrum Cortex

• Regulation of higher brain functions

• Gyri (bumps) and sulci (grooves) increases surface area

• Functional units are layers along surface

• Different functions are localized in different parts of the brain surface

Basal Ganglia

• Multiple nuclei located deeper in the brain

• Main conscious decision making center in the brain

  • Addiction and movement

• Dopamine modulates function

• When diseased can cause parkinson’s

Mechanoreceptors

• Ion channels that opne when stretched

• Typically part of larger sensory organs

• Important for touch, hearing, balance, and proprioception

Chemoreceptors

• Important for smell and taste

• When activated cells start to fire

• Specific to one type of signal

Thermoreceptors

• Important for temperature sensing

• Open at specific temperature ranges

• Main sensor for temperature regulation

• Localized through skin and hypothalamus

Electromagnetic receptors

• Important for vision, light reception, and magnetism

Specificity of sensors

• Sensory neurons only have one type of receptors

• In order for the brain to get a specific response neurons use only one type of receptors

Integration of signals

• Uses multiple neurons

Hearing and equilibrium

• Changes in the liquid in cochlea

• Hair cells along basilar membrane

  • the more they move the more amplified the sound is

• Allows us to detect frequency

• Volume how much movement there is in the hair cells

• Frequency which receptors are being found

How do cells detect light?

• Opsin receptors

  • All mechanoreceptors

  • Binds to ion channels —> change in electrical potential

• Bind to photons

• Even having just a ight sensitive cell that can be helpful

Mammalian Eyes

• Pupil: Lens that focuses the light

• Opsin receptors are located in the back of the eye

• Rods work well at low light intensity (night vision)

• Cones are optimized for high light intensity

• Cells —> action potential—> optic nerve—> brain—> thalamus (for processing)

How does light exposure affect membrane potential?

• Always release glutamate

• In the baseline (the dark), they release more glutamate

• Gradual change of glutamate from depolarization to hyperpolarization

How are light signals converted into changed firing patterns to the brain?

• Photoreceptors cells, bipolar cells, retina ganglia cells—> do integration

• In the middle of our retina one photoreceptor cell per one retina ganglia cell

• Higher ratio for the outside of your retina (many photoreceptors to one retina ganglia cell)

Color Vision

• Rods (night vision)

  • Sensitive to very low light intensities

  • Vast majority of photosensistive cells in retina

• Cones (daytime vision)

  • 2-4 subtypes

  • Requires higher light intensity

  • High spatial and temporal resolution

• Need at least 3 cones, rods do not impact color because it is too high of light intensity

• Fovea evolved so primates can see color

How does the brain perceive light information?

• Thalamus → Cortex —> opciptal lobe

• Conscious image forming

Non image forming pathways

• Used for non-conscious task

• Your mood can be impacted by non-image light pathways

• Thalamus —> instead go to lower brain areas (brain stem)

• Inside of some retina ganglia cells, melanopsin project to different areas in brainstem and hypothalamus

Spinal Cord

• Reflexes

• Neurons send signals to muscles

Brainstem

• Breathing, heart rate

• Turning your head

• Unconscious

Cortex

Conscious

Monosynaptic relfexes

• Simplest and fastest reflex

• One synapse in spinal cord

• Only positive signals

• Super fast

Polysynaptic reflexes

• At least one interneuron in spinal cord

• More synapses = slower

• Move complex integration

• More complex —> slower the response but more refined

Joint receptors

• Provide information about the positioning of joints

• Measures the position of your joints (angle)

Golgi tendon organs

• Neuron fibers interwoven through tendon

• Sensor fires when tension on tendon increases

• Inform your brain on how much pressure is on your muscles

• Protects your muscles from too much pressure

Muscle spindles

• Located between muscle cells

• Spindles consist of sensor and small muscle

• Sensor increases firing in reposne to strenching Increased stretch results i muscle contraction

Voluntary control of movements

• Execution: CPG

• Planning: Prefrontal and sensory cortex

• Initiation: Brain stem, motor cortex, basal ganglia

• Feedback: Cerebellum, sensory cortex