Special senses

, Olfaction, Equilibrium, Gustation and vision

Vision: 3 tunics from superficial to deep

a.    Fibrous Tunic 

b.    Vascular tunic

c.    Nervous tunic 

Fibrous tunic

1.       Sclera

     2.       Cornea

Sclera

Cornea

(avascular and transparent): Dense regular connective tissue, has fewer fibroblasts than the sclera, more elastic fibers than collagenous fibers, and contains less water.  Anterior corneal epithelium (stratified cuboidal non mucous epithelium)

Vascular Tunic

1.       The choroid

2.       Ciliary Muscle

3.       Iris

The Choroid

Ciliary Muscle

Iris

1)    Sphincter pupillae : Postsynaptic parasympathetic Ach binds to excitatory muscarinic cholinergic receptors causing inward contraction

2)    Dilator pupillae: Postsynaptic sympathetic NE binds to excitatory alpha 1 adrenergic receptors.

Seeing Near

◦     Ciliary muscle contracts inward, bulging lens; parasympathetic.

◦     Iris sphincter pupillae contracts inward, constricting lens; parasympathetic.

◦     Medial rectus skeletal muscle involved in somatic reflex; rotates eyes medially.

◦     All three of these steps are collectively called accommodation

◦     For far the reverse of the above happens

The Lens

Three types of sightedness

1)      Presbyopia

2)      Hyperopia

3)      Myopia

Presbyopia

Hyperopia

Myopia

Near sightedness Elongated eyes in an anterior/posterior direction. Concave lens correct myopia by the outward refraction the light and causing the focal point to land farther back.

Astigmatism is an irregularity in the shape of a lens

The Nervous Tunic

1)    Pigmented epithelium of the retina

2)    Sensory retina 

Pigmented epithelium of the retina

Sensory retina (Neural layer of the retina)

i.              Photoreceptor layer: (Rods and Cones). Bipolar neurons

ii.            Bipolar cell layer:

iii.           Ganglion cell layer: Unipolar afferent neurons

Outer and Inner Segments

Dendrites of rods and cones. They’re linked by a nonmoving cilium. In the light, rods and cones are inhibited. They cannot secret neurotransmitters in the day.

Vitamin A

Vitamin A is converted to either rhodopsin (rod photo pigments) or iodopsin (1 type of cone photo pigments).  [3 types of iodopsin: red, green and blue.]

Rhodopsin is a colorless glycoprotein plus a molecule of retinal.

When retinal is curved, (in the dark) it is called 11-cis retinal.

In the dark and light, 11-cis retinal + glycoprotein = a G- protein linked receptor. In the dark, rhodopsin or iodopsin wouldn’t be linked to the gamma protein.

Transducin: Are the three G proteins.

In the dark

In the Dark

In the Light

Visual Pathway

Light entering each eye strikes the rods and cones dendrites in the retina. Aps along each optic nerve, Transition from PNS to CNS at optic chiasm, Aps along each optic tract. Optic tracts conduct Aps to the thalamus and the superior colliculi of the corpora quadrigemina. Aps travel to primary visual cortex of each occipital lobe. Partial decussation occurs at the optic chiasm. L&R Visual field: Anterior surface of each cornea.

Temporal & Nasal ganglion cells

The temporal ganglion cell axons do not decussate. The nasal ganglion cell axons however do decussate at the optic chiasm.

Visual Pathway

L occipital lobe cortex receives input from medial half of LVF and Lateral half of RVF (right visual field). R occipital lobe cortex receives input from the medial half of the RVF and lateral half of the LVF.

20:1 ratio of rods to cones. (120 million vs. 6 million in each retina)Rod cells are light-intensity sensitive. They’re more peripherally located.

Cone cells are more wavelengths sensitive. They’re better than rod cells at visual acuity. Central fovea: (nothing but cone cells).

Electro-magnetic spectrum: From Gamma radiation to radio waves.

Skeletal muscle

A skeletal muscle is an organ

Deep fascia

Epimysium

Perimysium

Endomysium

What is a sarcolemma?

• The cell membrane of muscle cells.
• From Greek for “fleshy sheath”.

What are T tubules?

is the sarcoplasmic reticulum?

• Modified smooth endoplasmic reticulum.
• It’s sole purpose is to store Ca²⁺ ions.
• From Greek for “Network of Fleshy Material”

What are myofibrils?

• Highly modified cytoskeleton.
• A myofibril is as long as the entire muscle cell.

What is an I-band?

• I stands for isotropic; does not polarize light.
• It is bisected by a Z-disc.

It is composed of a Z-disc and a bunch of microfilaments

What is an A-band?

• The space between two I-bands.
• Composed of a bundle of thick myofilaments.
• A stands for Anisotropic; does polarize light.

End Plate Potential

a kind of EPSP, but the postsynaptic cell is a muscle cell.

Prior to the formation of cross bridges, myosin heads hold ADP and an inorganic phosphate. Summation of EPSP brings sarcolemma to threshold voltage, Ap along sarcolemma and T- tubules. Vg Ca2+ channels along the SR open, and Calcium ions are secreted and bind to troponin to cause a conformational change. Myosin heads of thick filaments form cross bridges with actin of the thin myofilaments. 

End Plate Potential

Upon cross bridge formation, the inorganic phosphate is released, Myosin heads bend inward (towards the center of an A-band); the low- energy conformation state. ADP is released at the end of the power stroke. Cross bridge remains until another ATP is bound. Cross bridge detaches after an ATP takes the place of the released ADP and the ATP is hydrolyzed into ADP and phosphate, and the myosin is bent outward (recovery stroke). Power stroke (myosin head bends inward). Recovery stroke (myosin head bending outward after contraction)

All of the sarcomeres contract fully or none of them do despite the individual formation of cross bridges.

Motor unit

One somatic motor neuron plus all of the skeletal myofibers it innervates

Relaxation

Relaxation

No more Ca2+ troponin complexes, Troponin returns to its original conformation, Tropomyosin covers the actin attachment site. Assuming dry room temp, Rigor mortis begins 2-3 hours after death, peaks at about 12 hours after death and ends completely 2-3 days later.

Following death, there’s no more ATP production, very little ATP storage, so free ATP is used up in a few seconds. No primary or secondary active transport of CA2+, Ca2+ binds to troponin; myosin head bind to actin protein forming cross bridges. Hence muscles contract fully and don’t return back to normal due to lack of ATP.

Assume a strenuously exercising muscle

1)    Free ATP used up in seconds

2)    ATP formed by creatine phosphate (aka phosphocreatine)

3)    CP + ATP -----> <----------------- (creatine kinase)=  Creatine + ATP

4)    ATP formed by aerobic respiration C6H12O6 +6O2+2ATP à 6CO2+6H20+KINETCI ENERGY TO FORM 40 ATP.

5)    38 ATP formed in total.

6)    Aerobic respiration in relaxed muscle cells tends to utilize fatty acids to make ATP

Assume a strenuously exercising muscle

1)    Glucose enters by fac. Diffusion & by secondary active cotransport with Na+

2)    Relaxed muscle cells store glucose in form of glycogen

3)    Myoglobin binds O_2.

4)    Exercise: myoglobin releases O₂ (for aerobic respiration) we also have O_{2 –}diffusing into the cell.

Glycolysis: the beg

Lactate Fermentation

Glycolysis converts C₆H₁₂O₆ into 2 pyruvate ions and forms 2 ATP profit. Fermentation converts the pyruvate ions into 2 lactate ions & coenzymes needed for continued glycolysis

Skeletal muscle cell types

1.    Type 1. Slow twitch oxidative fibers: Slowest to contract, narrowest in diameter, highest myoglobin concentration, most reliant on aerobic resp. Most resistant to fatigue.

2.    Type 2 x. (White fast-twitch fibers): quickest to contract, broadest in diameter, lowest in myoglobin concentration, least reliant on aerobic respiration, least resistant to fatigue.

3.    Type 2 (red fast-twitch fibers)

Smooth muscle cell

are spindle-shaped, much smaller than skeletal muscle cells, more fatigue resistant (than SK), not striated, mononucleated and involuntary. No z discs proportionally smaller sarcoplasmic reticulum. No sarcomeres. They are more reliant on extracellular Ca²⁺.

Thin myofilaments join to dense bodies (proteins) instead of z discs. 

Smooth Muscle cells

Most Ca²⁺ enters from outside (some released from SR). Ca²⁺ binds to Calmodulin. Myosin kinases phosphorylate (add a phosphate to myosin head). In its phosphorylated form, myosin heads bind to actin. Ca²⁺ pumped out of cell by Ca²⁺ ATPases and by secondary active counter-transport with Na⁺ . Without calcium, no more Calcium calmodulin complexes, a decrease in myosin kinase activity, decrease in phosphorylation of myosin heads. Dephosphorylation of myosin heads, causing detachment of cross bridges.

Types of Smooth Muscle

Visceral smooth muscle [single unit] characterized by gap junction proteins {functional syncytium}

1.    Multi-unit smooth muscle. E.g. erector Pilli muscle, ciliary ligaments etc. characterized by few if any gap junctions, one or a few contracting at a time. 

Anterior Pituitary

1)      Human growth hormone

2)      Thyroid- stimulating hormone

3)      Follicle- stimulating hormone

4)      Luteinizing hormone

5)      Prolactin

6)      Adrenocorticotropic hormone

7)      Melanocyte- stimulating hormone

Posterior Pituitary

1)      Anti-diuretic hormone

2)      oxytocin

Thyroid Gland

1)      thyroxine

2)      triiodothyronine

3)      calcitonin

Parathyroid Gland

Adrenal Cortex

1)      aldosterone

2)      cortisol

3)      androgens

Adrenal Medulla

1)      epinephrine

2)      norepinephrine

Pancreas

1)      insulin

2)      glucagon

Ovaries

1)      estrogen

2)      progesterone

Testes

Pineal Gland

Melatonin

Thymus

Endocrine system:  

Endocrine organs/tissues/cells secrete hormones which are circulating ligands.

Exocrine organs/tissue/cells secrete substances into a duct that connects directly to another organ. 

Chemical categories of hormones

Monoamines

Peptides

Protein hormones

Glycoproteins

Steroids

Fatty acids

Monoamines: 

1 or 2 amino acid molecules with a single amino group. An Amino group is NH₂. E.g. Dopamine, Serotonin, Melatonin, T_3, T₄, epinephrine, NE. All are water soluble, except T₃ and T₄ [which are lipid soluble]

a.    Catecholamines are monoamine hormones with a double hydroxyl group. E.g. NE, E, dopamine. 

Peptides: 

Protein hormones. 

Glycoproteins: 

Steroids: 

Fatty acids: 

prostaglandins, archidonic acid. All nonpolar and lipid soluble.

-       Hormones (i.e. endocrine secretions)

-  

 Autocrine secretions and Paracrine secretions are both secreted into interstitial fluid bind to receptors of nearby cells

E.g. T₄ Lymphocytes secrete an Autocrine protein called interleukin-2 (il-2)

T4 lymphocytes respond to IL-2 with mitotic cell division into helper T cells and memory T cells.  [SELF STIMUALTION]

Paracrine: Helper T cells secrete iL-2 onto a T8 lymphocyte, which responds with mitotic cell division into killer T cells and Memory T Cells. [Different cell type gets stimulated]

E.g. nitric oxide from epithelial cells lining blood vessels

Plasma Half-life:  

The amount of time required for the body to clear half of the hormone molecules in the circulation.

How to calculate plasma half-life:

a.    Inject a known amount of a hormone,

b.    Draw blood 30 minutes later and measure the plasma hormone conc.

c.    Continue to draw blood periodically and measure the hormone conc.

T4 has a plasma half-life of 6 days.

A constant, low level of a hormone in the blood typically results in the hormone’s target cell up regulating the number of receptors and vice versa for down regulating.

Permissiveness:  

One hormone causes up regulation of receptors for a second hormone.  E.g. FSH causes an up regulation of receptors for the glycoprotein LH.

Lipid soluble hormones diffuse across the phospholipid bilayer and bind to an intranuclear receptor, while water soluble hormones bind to membrane receptors (most are g-protein linked receptors)

Release of aldosterone [renin-aldosterone pathway]:

Drop in blood pressure, in response to the drop in BP, kidney arterioles secrete renin. Angiotensinogen binds with renin to form Angiotensin 1; Angiotensin 1 is converted by an enzyme [ACE {Angiotensin-converting enzyme}] to Angiotensin 2 in the lung capillaries. Angiotensin 2 is a systemic vasoconstrictor and a hormone. Angiotensin 2 binds to membrane receptors of specific cells in the adrenal cortex (cells of the Zona glomerulosa). P.s Adrenal cortex is divided into 3 layers. Z. Glomerulosa, Z. fasciculata, Z. reticularis. Z.g. cells respond to angiotensin 2 molecules by secreting aldosterone into the body’s circulation. Intranuclear receptor for aldosterone is found in principal cells of the kidney. Aldosterone receptor binds to DNA, causing the transcription of 2 mRNA. Up regulation of Na+ leak channels and Na+, K+ ATPases which makes the cells far more sodium permeable. Increase of Na+ reabsorption out of the renal filtrate and into the kidney capillaries. Plasma solute conc. increases. Increase in blood volume due to the absorption of Na+ from the urine, which increases the blood pressure. 

Hypothalamus produces 9 hormones.

-       ADH (Antidiuretic hormone)

-       Oxytocin

-       7 hypothalamic regulatory hormones. 

Hypothalamus produces 9 hormones.

ADH & Oxytocin neurons have axons leading down the infundibulum into the posterior pituitary gland. Oxytocin is a peptide that binds to membrane receptors of smooth muscle in the uterus and mammary gland triggering contraction.  ADH molecules bind to sudoriferous glands (sweat glands) for inhibition [losing less water by decreasing perspiration], blood vessel smooth muscle for excitation [ADH (Vasopressin) is a systemic vasoconstrictor]. When BP drops drastically, ADH then acts as a vasopressin. Dehydration, causes an increase in plasma solute conc. BP drops, ADH is released. ADH is a peptide that binds to membrane receptors of kidney principal cells forming a g-protein pathway that results in up regulation of aquaporins which increase water reabsorption and blood volume which in turn increases Blood pressure.

 Hypothalamic osmoreceptors fire Aps in response to an increase in plasma solute concentration.

7 hypothalamic regulatory hormones: 

5 releasing and 2 inhibiting hormones.

a.    GHRH: peptide that causes specific ant. Pituitary cells to secrete GH

b.    GHIH: Peptide that causes specific ant. Pit. Cells to not secrete GH.

c.    CRH: corticotrophin RH. Corticotrophin is also called Adrenocorticotrophic hormone (ACTH).

d.    TRH: thyrotropin RH. Thyrotropin is also known as Thyroid stimulating hormone.

e.    PRH: prolactin RH.

f.     PIH: prolactin IH. Monoamine aka Dopamine.

GnRH: gonadotropin RH. Peptide from hypothalamus that targets 2 different cell types in the ant pit. Which respond by secreting FSH and LH

ANT. PIT. HORMONES

HGH

TSH

ACTH

LH

FSH

Prolactin

Beta-endorphins

Lipoprotein

MSH

HGH 

(human growth hormone): a protein aka somatotropin targets many cell types. 

The target cells respond by secreting somatomedins (peptides that circulate or act locally). Which increases growth during childhood and teen years, increase healing/tissue repair during adulthood.  Increase in glucose and amino acid absorption. 

TSH 

(Adrenocorticotrophic hormone) a protein that targets the L & R adrenal cortex specifically the Zona fasciculata.  Increase in secretion of glucocorticoids especially cortisol inhibits ACTH and CRH secretion

LH

FSH 

(follicle-stimulating hormone) Ovaries respond by ovarian follicle maturation. Testes respond with increased sperm cell development.

Increase in testosterone, progesterone and estrogen will inhibit GnRH secretion.

Prolactin (PRL). 

Lipoprotein:

MSH 

Thyroid follicles 

T3 

T3 and T4 

PTH

Vitamin D formation:

1.    Exposure to UV rays, Vitamin D3 is absorbed by the body

2.    An enzyme called liver hydroxylase converts Vitamin D3 into cholecalciferol.

3.    PTH activates an enzyme called kidney hydroxylase.

4.    Active kidney hydroxylase converts cholecalciferol into active vitamin D aka calcitriol.

5.    Calcitriol is a co-enzyme needed for absorption of dietary Ca2+ in the small intestine. 

L&R adrenal medulla