chapter 4: sex differences in behavior: animal and human models examining the neural and...

Chapter 4:

Sex Differences in Behavior: Animal and Human Models Examining the Neural and

Neuroendocrine aspects of the Brain.

4.2 Synapses may form either on dendritic spines or on the shaft of a dendrite

4.5 Cichlid fish show changes in neuronal cell size in response to social conditions

4.8 Singing in female songbirds falls along a broad continuum

Santiago Ramon Y. Cajal (1852-1934)Founding Scientist in the Modern Approach toNeuroscience. Received Nobel Prize in 1906

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 11.1: The nervous system’s functions, p. 388.

Sensory input

Motor output

Integration



Figure 11.2: Levels of organization in the nervous system, p. 389.

Central nervous system (CNS) Brain and spinal cord Integrative and control centers

Sensory (afferent) division Somatic and visceral sensory nerve fibers Conducts impulses from receptors to the CNS

Motor (efferent) division Motor nerve fibers Conducts impulses from the CNS to effectors (muscles and glands)

Autonomic nervous system (ANS) Visceral motor (involuntary) Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands

Sympathetic division Mobilizes body systems during activity

Parasympathetic division Conserves energy Promotes housekeeping functions during rest

Peripheral nervous system (PNS) Cranial nerves and spinal nerves Communication lines between the CNS and the rest of the body

Somatic nervous System Somatic motor (voluntary) Conducts impulses from the CNS to skeletal muscles

= Structure= Function

Key:

Centralnervoussystem(CNS)

= Sensory (afferent)division of PNS= Motor (efferent)division of PNS

Key: Brain

SpinalcordSkin

Visceral organ

Skeletalmuscle

Peripheral nervous system(PNS)

Motor fiber ofsomatic nervoussystem

Somatic sensoryfiber

Sympatheticmotor fiber of ANS

Parasympatheticmotor fiber of ANS

Visceralsensory fiber

(a)

(b)



Figure 11.3: Neuroglia, p. 390.

(a) Astrocyte

(d) Oligodendrocyte

(e) Sensory neuron with Schwann cells and satellite cells

(b) Microglial cell

(c) Ependymal cells

Schwann cells(forming myelin sheath)

Cell bodyof neuron

Satellite cells

Nerve fiber

Capillary

Neuron

Nerve fibers

Myelin sheath

Process ofoligodendrocyte

Fluid-filled cavity

Brain or spinal cord tissue



Figure 11.4: Structure of a motor neuron, p. 392.

(b)

(a)

Dendrites(receptiveregions)

Cell body(biosynthetic centerand receptive region)

Nucleolus

Nucleus

Terminal branches(telodendria)

Nissl bodies

Axon(impulse generatingand conductingregion)

Axon terminals(secretorycomponent)

Axon hillock

Neurilemma(sheath ofSchwann)

Node of Ranvier

Impulsedirection

Schwann cell(one inter-node)

Neuron cell body

Dendriticspine



Figure 11.5: Relationship of Schwann cells to axons in the PNS, p. 394.

(a)

(b)

(c)

(d)

Schwann cellcytoplasm

Axon

NeurilemmaMyelinsheath

Schwann cellnucleus

Schwanncell plasmamembrane

Myelin sheath

Schwann cellcytoplasm

Neurilemma

Axon



Figure 11.6: Operation of gated channels, p. 398.

(a) Chemically gated ion channel

Na+

K+K+

Na+

(b) Voltage-gated ion channel

Na+

Na+

Receptor

Neurotransmitter chemical attached to receptor

Closed Open

Membranevoltagechanges

Closed Open

Chemicalbinds



Figure 11.7: Measuring membrane potential in neurons, p. 399.

Voltmeter

Microelectrodeinside cell

Plasmamembrane

Ground electrodeoutside cell

Neuron

Axon



Figure 11.8: The basis of the resting membrane potential, p. 399.

Na+Na+

K+K+

K+

K+

Na+

Na+

Na+

Na+

Cell interiorNa+

15 mMK+

150 mMCl–

10 mMA–

100 mMNa+

150 mMA–

0.2 mM

Cell exterior

K+

5 mMCl–

120 mM

Cellexterior

Cellinterior

Plasmamembrane

Na+–K+

pumpDif

fusi

on

K+ Na

+ Diffu

sion

-70 mV



Figure 11.9: Depolarization and hyperpolarization of the membrane, p. 400.

Depolarizing stimulus

Mem

bra

ne

po

ten

tial

(vo

ltag

e, m

V)

Time (ms)

0–100

–70

0

–50 –50

+50

1 2 3 4 5 6 7

Hyperpolarizing stimulus

Mem

bra

ne

po

ten

tial

(vo

ltag

e, m

V)

Time (ms)

0 1 2 3 4 5 6 7–100

–70

0

+50

Insidepositive

Insidenegative

(a) (b)

Restingpotential

DepolarizationRestingpotential

Hyper-polarization



Figure 11.10: The mechanism of a graded potential, p. 401.

(b)

Depolarized region Stimulus

Plasmamembrane

Depolarization Spread of depolarization(a)



Figure 11.11: Changes in membrane potential produced by a depolarizing graded potential, p. 402.

Distance (a few mm)

–70Resting potential

Active area(site of initialdepolarization)

Mem

bra

ne

po

ten

tial

(m

V)



Figure 11.12: Phases of the action potential and the role of voltage-gated ion channels, p. 403.

0 1 2 3 4–70–55

0

+30M

emb

ran

e p

ote

nti

al (

mV

)

Time (ms)

Rel

ativ

e m

emb

ran

e p

erm

eab

ilit

y

Na+Na+

K+K+

Outsidecell

Insidecell

Outsidecell

Insidecell

Depolarizing phase: Na+

channels openRepolarizing phase: Na+

channels inactivating, K+

channels openAction potential

PNaPK Threshold

Na+Na+

K+K+

Outside cell

Insidecell

Outsidecell

Insidecell

Inactivation gate

Activationgates

Potassiumchannel

Sodiumchannel

Resting state: All gated Na+

and K+ channels closed (Na+ activation gates closed; inactivation gates open)

Hyperpolarization: K+

channels remain open; Na+ channels resetting

2

2

3

4

4

1

11



Figure 11.13: Propagation of an action potential (AP), p. 405.

–70

+30

(a) Time = 0 ms (b) Time = 2 ms (c) Time = 4 ms

Voltageat 2 ms

Voltageat 4 ms

Voltageat 0 ms

Resting potential

Peak of action potential

Hyperpolarization

Me

mb

ran

e p

ote

nti

al

(mV

))



Figure 11.14: Relationship between stimulus strength and action potential frequency, p. 406.

Time (ms)

Vo

ltag

eM

emb

ran

e p

ote

nti

al (

mV

)

–70

0

+30

Threshold

Actionpotentials

Stimulusamplitude



Figure 11.15: Refractory periods in an AP, p. 406.

Stimulus

Mem

bra

ne

po

ten

tial

(m

V)

Time (ms)

–70

0

+30

0 1 2 3 4 5

Absolute refractoryperiod

Relative refractoryperiod

Depolarization(Na+ enters)

Repolarization(K+ leaves)

After-hyperpolarization



Figure 11.16: Saltatory conduction in a myelinated axon, p. 407.

Node of Ranvier

Cell bodyMyelinsheath

Distalaxon



Figure 11.17: Synapses, p. 409.

(a)

(b)

Cell body

Dendrites

Axon

Axodendriticsynapses

Axoaxonicsynapses

Axosomaticsynapses

Axosomaticsynapses

Soma of postsynaptic neuron

Axon



Figure 11.18: Events at a chemical synapse in response to depolarization, p. 410.

Synaptic vesiclescontaining neurotransmitter molecules

Axon of presynapticneuron

Synapticcleft

Ion channel(closed)

Ion channel (open)

Axon terminal of presynaptic neuron

Postsynapticmembrane

Mitochondrion

Ion channel closed

Ion channel open

Neurotransmitter

Receptor

Postsynapticmembrane

Degradedneurotransmitter

Na+

Na+

Ca2+

Action Potential

1

2

3 4

5



Figure 11.19: Postsynaptic potentials, p. 412.

Threshold

Me

mb

ran

e p

ote

nti

al

(mV

)

Time (ms)

+30

0

–70

–55

10 20

(a) Excitatory postsynaptic potential (EPSP)

Threshold

Me

mb

ran

e p

ote

nti

al

(mV

)

Time (ms)

+30

0

–70

–55

10 20

(b) Inhibitory postsynaptic potential (IPSP)



Figure 11.24: Types of circuits in neuronal pools, p. 422.

(a) Divergence in same pathway

(e) Reverberating circuit

(f) Parallel after-discharge circuit

(b) Divergence to multiple pathways

(c) Convergence, multiple sources

(d) Convergence, single source

Input Input

Output Output

Input

OutputInput

Output

Input 1

Input 2 Input 3

Output

OutputInput

Why Study Bird Song?

Bird song has been a classic behavioral response studied in animals to help us understand sexually dimorphic differences in brain organization.

By studying bird song and the neural and neuroendocrine basis of bird song, we can better understand the principles of how the brain organizes itself during development.

This information about bird song can then be used to understand and/or predict aspects of organization of the brain of other animals including in humans.

Major Regions of the Bird Brain Associated with Song:

HVC = higher vocal center

RA = robust nuclusu of the archistriatum

nXIIts = hypoglossal nerve

DM = dorsomedial region of the nucleus intercollicularis

ICo = intercollicularis

Syrinx = the vocal organ in birds that produces sound (equivalent to our larynx)

A typical bird syrinx.

4.9 The neural basis of bird song

Note that in birds with sexually dimorphic song abilities, these brain regions are typically much larger in males than in females of the species.

4.10 Singing in zebra finches is organized by estrogens but activated by androgens

4.11 The sonic organs are used by Type I male midshipman fish to attract females to their nests

The sonic organs are sound producing muscles attached to the swim bladder in these fish.

Type 1 males have well developed sonic organs (6x) compared to Type 2 males or females.

The Type 1 male is an aggressive male.

The Type 2 male has a “sneaker” reproductive behavior pattern and actually has roughly a 9x gonad:body mass ratio compared to Type 1 males.

4.12 Urination postures of domestic dogs

4.15 The frequency of rough-and-tumble and pursuit play (Part 1)

Study of Rhesus Monkeys The pseudohermaphrodites are females who received in utero exposure to exogenous androgens.

4.15 The frequency of rough-and-tumble and pursuit play (Part 2)

4.16 Contributions of activational and organizational effects of hormones to behavior

Known Brain Differences in Humans:

SDN-POA = sexually dimorphic nucleus of the preoptic area of the hypothalamus.

The volume of SDN in medial preoptic area is modified by hormones, among which testosterone is proved to be of much importance. The larger volume of male SDN is correlated to the higher concentration of fetal testosterone level in males than in females.

From Roger Gorski’s Lab at Yale University:

Coronal rat brain sections showing the SDN-POA

A: male; B: female; C: female treated perinatally with testosterone; D: female treated perinatally with the synthetic estrogen diethylstilbestrol.

INAH-3 = the third interstitial nucleus of the anterior hypothalamus

The INAH has been implicated in sexual behavior because of known sexual dimorphism in this area in humans and because it corresponds to an area of the hypothalamus that when lesioned, impairs heterosexual behavior in non-human primates without affecting sex drive.

It has been reported to be smaller on average in homosexual men than in heterosexual men, and in fact has approximately the same size as INAH 3 in heterosexual women.

The above information is based on Simon Levay’s work that was published in the journal Science in 1991.

LeVay S (1991). A difference in hypothalamic structure between homosexual and heterosexual men. Science, 253, 1034-1037.

4.17 Average sex differences in behavior often reflect significant overlap between the sexes

4.18 Congenital absence of the olfactory bulbs in Kallmann syndrome

Kallmann Syndrome - hypogonadism (decreased functioning of the glands that produce sex hormones) caused by a deficiency of gonadotropin-releasing hormone (GnRH) which is created by the hypothalamus.

Alternative names include:

hypothalamic hypogonadism

or

hypogonadotropic hypogonadism

Males with this condition have smaller than average testes, are infertile, and express anosmia (the inability to detect odors)

This is due to incomplete development of the olfactory bulb embryologically.

The lack of olfactory bulb development results in the lack of GnRH cell development (the cells in the olfactory bulb normally migrate during development to the hypothalamus

4.19 A possible sex difference in the corpus callosum

Corpus callosum - a structure of the mammalian brain in the longitudinal fissure that connects the left and right cerebral hemispheres. It facilitates communication between the two hemispheres.

This may explain certain sexually dimporphic right/left communication disorders are more prevelant in males than females….. such as ADHD, schizophrenia. This may also suggest why females may have greater verbal cognition and why some task performance skills are sexually dimorphic…

4.20 Performance on certain tasks favor one sex over the other

Females > Males Males > Females

Box 4.5 Hormones, Sex Differences, and Art (Part 1)

Box 4.5 Hormones, Sex Differences, and Art (Part 2)

Male

Male

Male

Female with CAH

Female with CAH

Female

Female

All drawings by children aged 5-7.

Congenital Adrenal Hyperplasia (CAH) - an autosomal recessive disease group resulting in mutations of genes for hormone production in the brain that guid the biochemical steps of production of cortisol from cholesterol by the adrenal glands (Corticotropin Releasing Hormone (CRH) or Corticotropin Inhibiting Hormone (CRIH)) CRIH is also sometimes called Atriopeptin.

Most of these conditions involve excessive or deficient production of sex steroids and can alter development of primary or secondary sex characteristics in some affected infants, children, or adults.

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