MCB 32- Human Physiology

External environment

parts of the body that are directly connected to the outside (skin, gastrointestinal system, urinary, respiratory, reproductive)

Internal environment

parts of the body not connected to external environment, although external materials can be brought across epithelial cells into blood cells and vice versa

Homeostasis

The body’s ability to maintain a relatively stable internal environment (eg, within the range of 37 °C, near pH 7). uses negative feedback to counteract stimulus

Covalent bond

sharing of electrons (either unequally/ polar or equally/ nonpolar)

Ions

transfer of valence electrons binds two molecules to make them fully charged. they dissolve in water, making them good conductors of electricity, and giving them the name electrolytes.

Acids

Molecules that release H ions in water (either strongly or weakly depending on if they fully lose the H or disassociate)

Bases

molecules that bind protons (H)

4 types of tissue

1. Epithelial (epidermis, glands, lining of GI tract and other hollow organs), have tight junctions

2. Connective (fat and other soft padding)

3. Muscle (skeletal, cardiac, smooth), contract and produce force

4. Nervous (neurons and their support cells/glia: brain, spinal cord, nerves)

pH

measure of how many H ions are in a solution to quantifiy acidity (<7 is acidic, more H, >7 is basic, less H)

Exocrine glands

secrete chemicals into external environment

endocrine glands

secrete hormones into bloodstream

microtubules

around cell membrane, support cell movement and muscle contraction. found in microvili

microfilaments

large parts of the cytoskeleton that provide track for transporting vesicles

Parameters that affect rate of diffusion

surface area, permeability, distance of diffusion, concentration gradient, size of molecule passing

Diffusion rate at body temp

At 37 C, the rate is proportional to the concentration gradient(surface area)(permeability) / distance

Secondary active transport

pump couples the flow of one substance going down gradient with another substance going against it. does not use ATP

Co transport (symport)

transport of two molecules going in same direction

Counter transport (antiport)

transport of two molecules in opposite directions

Paracrine signal

chemical messenger that diffuses locally and acts on a neighboring cell

Types of hormones

1. Peptide (lipophobic- like insulin, oxytocin)

2. Steroid (lipophilic- like cortisol, aldesterone, testosterone, estrogen, progesterone)

3. Amine (sometimes both but epinephrine is lipophobic)

Primary endocrine system (main fcn is to secrete hormones)

hypothalamus, anterior pituitary gland, thyroid, thymus, adrenal gland, pancreas

Secondary endocrine system

Heart, liver, stomach, kidney

tropic hormones

Hormones that stimulate the release of other hormones (most released by anterior pituitary gland, peptides (lipophobic))

explain how action potential releases NT

action potential causing VgCach to open, calcium goes down gradient, triggering release of synaptic vesicles with NTs, which bind to receptors in post synaptic cell

Types of membrane receptors in NS

1. Ionotropic/Ligand-gated ion channels (open and close for specific ion, used for faster, shorter responses)

2. Metabotropic/GPCRs (activate ion channels or use secondary messengers to activate ion channels. slower, but can change gene expression for longer-lasting effects)

2 types of neural signaling

1. Electrical (gap junctions, cell to cell)

2. Chemical (NTs)

How are NTs cleared from synaptic cleft?

Via reuptake channels, transported into glia cells to be reused, or destroyed by enzymes

2 types of graded potentials with examples

1. depolarizing/excitatory: open Na+ or all cation channels, close K+ channels to increase likelihood of action potential. eg: glutamine

2. hyperpolarizing/inhibitory: open K+ or Cl- channels to decrease likelihood or reaching threshold. eg: GABA

used for local signaling only (decremental). because graded potentials can summate and have different amplitudes, they can have multiple inputs (synaptic integration, either from two rapid synapses (temporal) or nearby synapses (spatial))

axon hillcock

integrator that adds up arriving signals (excitatory/inhibitory)- where threshold is met

Graded potentials vs action potentials

Graded: localized, variable electrical-strength signals, can sum, excitatory/inhibitory, in dendrites/ cell body (soma)

Action: non-decremental, all-or-none electrical signals triggered by reaching threshold from graded potential, have refractory periods, in axon

CNS

• made of brain and spinal cord, which integrate information and initiate actions

PNS

made of neurons going into afferent/sensory neurons our out of efferent neurons

Afferent nuerons

Sense (aka sensory neurons) external environment and signal CNS

Efferent neurons

‘Exit’- transmit information out of CNS to peripheral neurons

Interneurons

only in CNS, do most of processing

blood brain barrier

separates blood from CSF to protect CNS from harmful substances in blood, made up of glia cells called astrocytes. these have tight junctions for extra protection to prevent crossing.

meninges

connective tissue that protects NS

Cerebrospinal Fluid

CSF: fills space between meninges and in cavities in the brain called ventricles to protect the brain from hitting the skull. CSF also serves as a reservoir for the brain’s interstitial fluid, so it has correct extracellular ionic concentrations and provides neural cells with essential nutrients via the circulatory system. 

Dorsal/ventral

dorsal= side facing back half of body

ventral= side facing front/belly

dorsal root ganglion

collection of sensory neuron cell bodies outside of spinal cord

dorsal/ventral root

Sensory neuron axons (afferent) enter the spinal cord via the dorsal root and the motor neuron axons (efferent) leave via the ventral root

Corpus callosum

axons that connect the left and right sides of cerebral cortex (white matter bundle)

diencephalon (thalamus and hypothalamus)

Thalamus: relay station for sensory information

Hypothalamus: maintaining homeostasis

Brainstem and its parts

Brainstem: connects to spinal cord, regulates ANS, other unconscious functions

• Midbrain: controls eye movement, orienting head to sound/sight

• Pons: controls sleep, breathing, swallowing, etc

• Medulla oblongata: controls blood pressure, breathing, etc

Frontal lobe

Executive function, decision-making, problem-solving, personality, motor control

Parietal lobe

Sensory perception (touch, pain, temp), spatial awareness, attention

Temporal Lobe

Auditory processing, memory, language comprehension, emotion

Occipital Lobe

Visual Processing